Original subtitles

[dramatic music]

- [Narrator] In 1941,

the Nazis take over a Renaissance castle

and begin to make ominous changes.

- They really took this structure and altered it

to suit a super secretive motive.

- [Narrator] Behind opulent walls,

strange retrofitting takes place.

- It's really not the ideal installation

from a military point of view.

Why do we have this castle?

- [Narrator] And below the castle,

a massive underground tunneling project is taking shape.

- Something much bigger

than just renovation is taking place.

- [Narrator] Why would the SS be so interested

in a building so vulnerable?

- You can see it from the air.

It's literally a little sign saying,

"Hey, here might be something important here."

- [Narrator] What dark secrets

could be buried underneath Castle Ksiaz?

[dramatic suspenseful music]

[dramatic music]

Located in modern-day Poland,

Castle Ksiaz would appear

to be a typical European Renaissance castle.

- That castle is massive. It's an impressive structure.

- [Narrator] Filled with the opulence expected of royalty.

- This is a stunning Baroque castle.

As you come through the hills, you start to see it emerges

from the gloom, from the mist,

and it literally takes your breath away.

- [Narrator] But behind these walls lie anomalies.

Secret staircases, passageways,

and massive tunnels belie this residence.

In 1941, the SS seizes the castle

and set about massive renovations.

- What on earth did the Nazis want

with a 13th century castle?

It seems like a very strange decision

and very unlike many of the other Nazi structures we're

more familiar with.

- [Narrator] At this time in the war,

the Nazis were furiously fortifying the width

and breadth of the Third Reich.

Bunkers, command nests,

and massive defensive structures dot the continent.

But their interest in this castle is very different.

- So by the time Adolf Hitler takes power,

this area has been in German control for centuries.

It's part of the Silesian district.

So today, this area is in Polish hands,

but when Adolf Hitler came into power, this land,

he would've seen this as ethnically German,

as German as German could be.

- Caste in fortified position has been here

since the 13th century and it belonged to a succession

of kings and princes and, in the 16th century,

landed in the hands of the Hochberg family.

- It was one of the richest family in the Germany.

- They run afoul of the Nazis.

The heir of the castle ends up

marrying a British aristocrat.

- [Narrator] Born Mary Cornwallis-West,

she became known as Princess Daisy of Pless

when she married into the Hochberg dynasty.

But her story ends in mystery.

- She was related by marriage to Winston Churchill.

She was an English woman, and she had married

into this very high-ranking German aristocratic family

and had moved to Germany, and she lived a very fancy life.

She was at one point deemed to be one

of the most beautiful women in Europe.

- [Narrator] Castle Ksiaz was the summer residence

of Princess Daisy, her husband,

Prince Hans Heinrich XV, and their three sons.

- One of the sons decides that he's going to move to the UK,

and he actually ends up joining the British Army,

and then his brother goes and joins the Polish Army.

- [Narrator] With two sons firmly in allied camps,

the SS became increasingly suspicious of the family.

- They would have known that she was an English woman.

They presumably knew about her connection to Churchill,

and in the 1930s, one of her sons was actually taken

into Gestapo custody and tortured.

She had to pay a large ransom to get him back,

but he actually died of his injuries.

So she was no friend of the Nazis and, in fact,

became targets for the Gestapo

and for the Nazi Security Services.

- So the Nazis seize their castle.

- We know that the Nazis were looting

and stripping assets as they advanced through Europe.

But for some reason, they've decided to occupy this castle.

[dark dramatic music]

- Everything inside, art, paintings, sculptures,

they took it away, secure somewhere.

- Part of the mystery is we don't know what happened

to a lot of the objects inside the castle.

The legendary Princess Daisy Pless pearls,

an alleged 20-foot-long pearl necklace,

invaluable, maybe one of the largest,

most expensive pearl chains or necklaces in history,

and it disappeared.

- [Narrator] Sometime after the Nazis take over the castle,

the princess dies under mysterious circumstances.

- And there's a story that her servants had

to hide her body.

They buried her in an unmarked grave,

so we still don't know where she was buried.

And for a long time, there was a rumor

that she had been buried wearing the pearls.

- [Narrator] Where the German police actually

after this priceless item?

Recent research claims that Daisy actually sold most

of her pearls before the Nazis arrived,

but it remains a family secret to this day.

So you still have treasure hunters around the area

and around the castle trying to find out

what happened to Princess Daisy's pearls.

- [Narrator] With the former royals out of the picture,

strange changes are immediately made to the building.

- The Nazis take this castle,

and they change it to suit their aesthetic.

They stripped it of some incredible features,

some various architectural elements

that they plastered over, essentially,

to tone down the extravagance of it.

- One of the best examples of this is the ballroom.

You walk in now, it's a simple ceiling.

What you don't realize is that Nazis plastered over.

It was once an elegant, ornate octagon ceiling.

They're trying to reimagine this castle, reenvision it.

Reenvisioned is part of this new Third Reich.

- [Brooke] From the outside, it's a big, beautiful castle,

and inside it tells a really different story,

pretty stark and definitely not a warm, welcoming feeling.

- [Piotr] Maybe in 1941 or 1942,

the Organisation Todt arrived and start

to adopt it for their own purposes.

- Organisation Todt

was effectively the Nazis' construction company

during the Second World War,

and they built tunnels and bunkers right

across the Third Reich.

- They were staffed with some of the best engineers in all

of Germany and given a virtually unlimited budget.

- And for them to be involved here

on this castle project meant that whatever it was,

it was hugely important to the senior Nazi command.

- 'Cause at one stage, it's thought of

as a potential location for the Ministry of Foreign Affairs.

And you have to ask yourself, why would that be?

Why would they want to place that important ministry

so far away from the center of power,

the gravity of power, Berlin?

And that begs the question,

is this something else that the Nazis are planning

for this location that we don't yet know about?

- [Narrator] One witness, Dorota Stepowska,

still recalls the mysterious comings

and goings of the Nazis once the castle is taken over.

She remembers it as the beginning of a dark period.

[speaks in foreign language]

- [Rob] But the Third Reich has castles all over the place.

For centuries, German princes and states

had been building castles of various forms.

- [Narrator] Could this sink be a propaganda move

on behalf of the Nazis?

- The castles were, I think, a draw

and an attraction because it was a reminder

of the greatness of Germany's past.

- [Narrator] Hitler and the Nazi Party tapped

into the nationalism festering

inside a humiliated and angry post-World War I Germany.

- [Deborah] By setting themselves up in a castle

that had a very long historical pedigree in Germany,

they were linking themselves to a celebrated Germanic past.

- [Narrator] But the massive presence of the SS

and large secretive projects seem to negate this theory.

Within the castle, features added included a guard room,

room replacing or adding several staircases,

modernized rooms, communication equipment, bunkers,

and an elevator that leads far below the castle.

[dramatic music]

- This is quite clearly not a good defensive site.

Back in its day, yes, it was.

That's what it was built to do,

but its walls stand absolutely no chance

against Second World War weaponry.

- These castles were built to be a castle.

They weren't designed to be a bunker.

They weren't designed to any sort of Nazi standard.

It was built as a castle.

They're fancy houses for wealthy people to live in,

not necessarily to withstand any sort of attack.

If you had a distinct plan, if you knew what you wanted

to do and where you wanted to go

and why you wanted to go there,

starting from something that's already there,

that isn't fortified, that isn't up to your standards,

that doesn't suit your aesthetic,

is a strange way to approach it.

- It's not an ideal facility the way it's constructed

to do a lot with it.

You have to make a lot of modifications.

It's almost better from a military point of view

to construct a brand new building

that has modern communication systems,

modern electric vacation.

It's very difficult, if not impossible,

to build on top of those existing structures

'cause they're not really designed to take additional loads.

So there's a lot of engineering and thought

that needs to go into redesigning these type of buildings

to make sure we're not compromising them

and to actually upgrade them.

It's not a straightforward process.

- [Narrator] Even as a young girl,

the surviving witness remembers clearly the attempts

of the Nazis to hide much bigger construction

than simple renovations.

[speaks in foreign language]

- The thing you have to realize about the Nazis

is that they were genuine masters at concealing

what was important to them.

So everywhere we go, we can find evidence

that they really understood that they had

to protect their key military sites,

and yet there's no extensible military value to this.

[laughs] For anything else, you can see it from the air.

It's literally a sign saying,

"Hey, there might be something important here."

- The challenge for them is this castle

was a public landmark,

one the most beautiful in that region of Europe,

sitting atop a majestic hill.

- This castle goes completely

against the Nazis' obsession with secrecy.

This building is very well known,

and dignitaries have come to visit this for years.

There would've been photos taken of the inside.

There's something odd going on here

unless the castle itself is just a decoy

and it's actually what's going on inside

and underneath the castle that's important to the Nazis.

- [Narrator] Unearthed documents, witness testimonies,

and recent excavations begin to pull

back the curtain on much darker plans.

- And then you discover that,

underneath that castle, there's a secret.

[dark dramatic music]

[soft dramatic music]

- [Narrator] In 1941,

German forces begin a full-scale renovation

of Castle Ksiaz.

Shrouded in secrecy,

they've not only modernized this Renaissance building

but also begin a massive construction project.

- Something much bigger than just renovation

is taking place underneath this castle.

- [Narrator] Construction underneath the castle itself

provided the perfect cover.

Even if allied planes flew overhead

between the massive building and surrounding forest,

no one would see the underground project.

And with extreme security around the complex,

spies couldn't get a look inside.

- They start to build a huge underground structure

below the castle.

- Tunneling is not an everyday construction project.

Tunneling is a very highly specialized project

with highly specialized, skilled workers from the design

of it to the pre-engineering to the construction of it.

- [Narrator] World War II expert Patrick Ney

has investigated many secret Nazi structures,

but this is something very different.

- [Patrick] Whatever's out there,

it must've been important enough

to blast a hole through the rock.

Sounds like a river.

[water rushes in distance]

Was this an escape tunnel,

or when the Nazis bringing something in here?

- [Narrator] With so few surviving witnesses

and the Nazis' scorched earth policy

of destroying documents,

experts must rely on excavations and archeology

to unravel the secrets of the castle.

- It's only relatively recently

that we've been able to get access to the castle,

access to the tunnels, and start to explore what's here.

You see the rock that they've bored into,

this is the igneous rock.

- It's really hard. That's hard rock.

You can't get through that without blasting.

[speaks in foreign language]

- The tunnels under this are gigantic.

You can drive a train into some of these.

These are impressive, some of the biggest

and most impressive in Europe.

- This tunnel is 175 feet below the courtyard.

Now that's deeper than most subway tunnels.

- [Narrator] Researchers even discover secret passageways

that connect the tunnels back up to the courtyard.

- Escaping down these stairs and in these tunnels,

deep underground in a mountain with hard rock,

that would be bomb proof.

- [Narrator] But unlike most other Nazi excavation projects,

building this system

underneath the castle created unique challenges.

- When we built in the 13th century,

we're taking relatively large stones,

shaping them to a shape,

stacking them on top of one another,

and putting probably an extremely weak mortar

in between, if anything, at all.

- The original construction was likely made out of rocks

and masonry, thousands of hours of construction

to build these solid rock foundations, essentially,

and all the way up with masonry.

- It's impressive to me because of so many unknowns

that would've had to be addressed

before starting such a project.

Adding to a house on the side is a different project

than digging underneath a castle.

- Digging through solid rock would've been hard enough,

but digging underneath a castle,

it had to have been extra sensitive

to all that weight above.

Some theories suggest that certain parts of the castle

were replaced to lessen the weight

that sat over the tunnels down below.

Now, could this be why one of the marble staircases

was replaced with a wooden one?

- [Patrick] Why would you need

to have this many smaller tunnels off this main shot?

- This was a massive project and yet there

are nearly no documents that survived to explain

what was planned here, which is strange,

and it also makes it very difficult

to say what this place was for.

- [Narrator] One challenge facing those

who would unlock the castle secret

is the years under the Iron Curtain

after the defeat of Nazi Germany.

At the end of the war, the area fell into Soviet hands.

Control over Lower Silesia

was transferred from Germany to Poland.

- And then Poland, occupied Poland, as it now is,

lies in the Iron Curtain, which means that the whole region,

the castle itself, is shrouded in mystery.

In fact, it lays abandoned for decades.

So when the castle and the region fall in Soviet hands,

they take anything that's useful back to Russia.

Any documentation they found would've been taken back.

That documentation has been under lock and key,

never shown the outside world ever since,

lying for quite literally decades.

So the question is, what could we find out

if we could get access to the real documentation lying

somewhere in Moscow?

- [Narrator] As recently as 2017,

these forgotten passageways were inaccessible

to researchers and the general public.

Immediately, a rush of experts clamored

to unblock caved-in tunnels

and unearth the castle's secrets.

- Comparisons to the concrete tunnels,

they look quite well developed.

This is pretty scary.

One thing is very clear. [laughs]

They were interrupted in their building.

You can see the roof over here.

It's not been developed at all,

so this is probably a tunnel that's not being completed yet.

[slow dramatic music]

- [Narrator] Slowly, as excavations reveal more

of the tunnels and underground structures,

new theories on the purpose of the castle come to light.

- Certainly, if I'm occupying a castle as a military group,

I wanna have some place that is safe.

So I might wanna build safety bunkers below ground

in case the castle destroyed,

egress routes beyond the castle grounds from those tunnels.

So they could've been simply a method to protect

against air raids in an attack.

- [Narrator] But the size and extent

of the tunnels go way beyond what is typical

for mere escape routes or air raid bunkers.

The scope of the project, the secrecy,

and the effort involved leads many experts

to believe this facility was far more

than a simple administrative building

with defensive bunkers.

- What we do know unequivocally

is how it was built, using forced labor,

under the most horrific of circumstances.

- What the Nazis did all across Europe

was repeatedly use concentration camp labor.

- Over 3,000 workers are said to have been slaving

away here in terrible conditions.

- This castle and whatever

was happening underground were so important

that the Nazis built a satellite concentration camp next

to it so that there would be a built-in workforce

to do all the work on the castle and below grounds.

- [Narrator] The use of slave labor also helps

to explain why we have so few witnesses

to the work done underneath Castle Ksiaz.

- For those Germans who had worked on the project

and did survive, they were not interested

in sharing those stories or implicating themselves

in possible crimes.

If you admitted that you had worked on this project,

if you had been involved in it,

if you had intimate knowledge of it,

you may have been setting yourself

to be exposed as a war criminal.

- [Narrator] For years, the shroud of secrecy

around the tunnels underneath Castle Ksiaz

has obscured investigator's abilities

to discern the true nature of this Nazi project.

But when research reveals the architect of the project,

experts wonder if the castle was meant

for the most important figure in the Third Reich.

[crowd roars] [dramatic music]

- Could a clue to this site be its architect,

Hermann Giesler?

He was a director in Organisation Todt

that built many of the Nazi bunkers,

but he also designed a house in Munich for Hitler.

- [Narrator] Massive Nazi tunnels and secret passageways

underneath a Renaissance castle in modern-day Poland

spark the curiosity of researchers.

As blocked caverns are slowly excavated

and documents unearthed,

an important figure enters the picture.

- One of the ideas that people have set forth

is that this place makes a natural headquarter

for the Fuührer.

- It has the makings of everything you'd want to have,

rapid access, rapid egress from the tunnels,

a very luxurious palace-like atmosphere,

and some type of vault at the lowest levels

to store important materials that may be needed

by either the Fuhrer himself

or other elite within the Nazi party.

- [Narrator] As investigations continue,

the elevator shaft added to the castle

connects the tunnels deep below the building

to a room supposedly intended for Hitler.

But some experts still questioned the high visibility

of the famous site.

- When you compare the castle here to the Wolf's Lair,

where Hitler spent the vast majority

of the Second World War, you can see a lot of differences.

The Wolf's Lair is in the forest, like the castle here,

but it's underneath a tree canopy

whereas the castle is very, very visible,

and the Wolf's Lair is completely invisible.

You can't see it from the air.

The whole thing was completely designed to make sure

that no one knew that Hitler was there,

and that's perhaps why he decided

to spend so much time there.

This guy doesn't think that he's safe.

- Why were they pouring so much effort and energy

into something this big when they had other residences

that Hitler was actually using on a regular basis?

- It doesn't seem at first glance to be the natural place

to put Hitler until you think about one thing.

Everywhere Hitler goes,

the entire German war machinery needs to come with him.

We're talking about thousands of people,

and this is place could've housed all of them and more.

And of course, in the unlikely event

that the allies would've attacked,

Hitler could've gone straight down in less

than a minute and been in the tunnels.

- As the Soviet union is pushed back

and as Nazi Germany expands its empire eastward,

this castle would be more centrally located

in the larger Germani, of the larger Nazi empire.

So from that perspective, it makes some sense.

- Hitler didn't really like being in Berlin very much.

He tended to run the government for months

at a time from one of the Fuhrer headquarters.

So he was often in Bavaria. He was often at Wolf's Lair.

So if he was going to be at this residence

for long periods of time, you're effectively trying

to make space for an entire government.

So the scale of it would fit with that set of priorities.

[dramatic music]

- [Narrator] Some experts believe the actual dimension

of the tunnels could provide proof of this theory.

- The size of this, absolutely extraordinary.

This is serious effort. This is no air raid shelter.

This area is not only isolated,

but it's well connected by rail.

So is it possible that this castle could've been designed

in the future, maybe they never got round to it,

to take Hitler's 17-car personal train?

The tunnels in this region would've been perfect

for Hitler's personal train.

- We do know that additional rail and additional roadways

were built leading to this castle

to accommodate something the size of the Fuhrer train.

- [Narrator] One of the most famous vessels Hitler used

during his reign, the Fuhrer train,

was initially named Fuhrersonderzug Amerika

because of his fascination with the United States.

It was later renamed Brandenburg

after the United States entered the war.

Before the first permanent Fuhrer headquarters was built,

the train served as a mobile headquarters,

and even after Germany entered the Balkans,

Hitler traveled on it often.

The train weighed 1,200 tons,

and its maximum length could reach 1,400 feet,

but this was ordinary train.

It contained two locomotives to guarantee function,

even in the event of an engine failure.

Two Flakwagens or special armored anti-aircraft cars

on each side of the train equipped

with Flakvierling 38 quadruple tube cannon

with a range of nearly three miles,

a number of baggage cars, Hitler's personal car,

a command car, including a conference room

and communication center, a security force car,

multiple dining cars, press car, two cars for guests,

a Badewagen, or bathing car,

and sleeping cars for personnel.

The trains were so critical to Hitler

that special bunkers were built to house them.

Following their leader, many of the Nazi's top command,

like Goring and Himmler, commissioned their own train.

To ensure security, much of the train's documentation

was destroyed after each use.

And in May 1945, after Hitler's suicide,

the SS blew up much of the train.

- If all this construction was indeed meant for Hitler,

then how come he never visited the place?

- For decades, people have been talking about

what exactly the Nazis were doing here,

and [laughs] everybody seems to have their own theory.

Local people had no idea what was going on here.

It would've been fenced off, barbed wire,

sentries, soldiers, all, of course,

with the express purpose of making sure

that the outside world has no idea what's happening.

Even some people in the German war machine

had no idea what was going on here.

If this was an ordinary complex part

of the overall German war machine,

then it would've come under the purview of the Wehrmacht,

the German military forces.

But it's the SS, Hitler's special troops,

under the command of Heinrich Himmler,

who was supervising the work that's going on here.

This means that it's very important

to somebody high up in the German war machine.

Part of the mystery of this castle

is actually by design, not by accident.

So there were probably people in the SS

who didn't want anyone else in Germany know about this.

It's even said the Albert Speer,

who was the German armaments minister,

didn't know what the exact purpose of the tunnels

that were being built here were.

- Albert Speer wrote after the war,

it was supposed to be a regional administrative center

with the Fuhrer headquarters and industrial facilities.

But people don't necessarily believe him

because he often was suspected of trying to throw people

off the trail or trying to make himself look good.

- [Narrator] After the death of Fritz Todt at 1942,

Albert Speer took over as the head

of the Todt Organisation.

Could the work on Castle Ksiaz had been so secret

that not even the German minister responsible

for its construction knew

about the true purpose of this project?

- They may not have even wanted Hitler to know about it.

After all, We know the Hitler never came here.

Perhaps he didn't realize the importance

of this castle to someone in the SS.

- Or could the SS be emptying the castle

and creating these tunnels to store something else?

- [Narrator] Lower Silesia, World War II.

Someone in the German high command

orders a massive renovation

and tunneling project at Castle Ksiaz.

It is later claimed that the castle was to be used

as a residence for Adolf Hitler.

But does the evidence support this theory?

- If you try to imagine what these tunnels represent

as a Fuhrer bunker, it's not really consistent,

meaning that other Fuhrer bunkers are considerably smaller,

far more austere, I suppose.

They're not as cavernous. They're not as massive.

But it's more consistent, I think, with other purposes.

- There are few survivors, inmates who originally worked

at Castle Ksiaz during World War II,

and because of the testimonies,

they are persuading off the researchers

that there must be some camouflaged tunnels.

- Witnesses and documents describe vast amounts

of crates and boxes being delivered here,

but no one knows what was inside them.

[dark brooding music]

- [Narrator] Using the castle to disguise the SS intentions

has experts coming up with theories

that even Hitler may not have known about.

- We know that Nazi Germany

was looting on an industrial scale,

billions and billions of dollars of material,

art, jewelry, gold.

Anything of value is stolen,

and we also know with absolute certainty

that not everything has been returned.

- One of the things that the Germans had done

as they swept through many major centers

in the Soviet Union in the first half of the war

was to take everything they could get their hands on.

- [Narrator] Towards the end of the war,

as the Third Reich shows signs of collapse,

many in the SS begin to plot their future post war,

and some didn't want others to know their plans.

Now, as the SS steal all of these things,

they have another problem to solve,

which is where on earth do they hide it.

- There's numbers of sites that we know

that were set up for this purpose alone.

- [Narrator] A rumor diary said to be held

by Freemasons after the war is attributed

to an SS officer who outlined 11 sites the Nazis used

to hide stolen goods.

- Millions of pieces of artwork, sculpture,

paintings, you name it, they had looted

from every single corner of occupied Europe.

- Renoir. There is Pissarros.

There is even Michelangelos that are still missing

- Almost one million pieces, masterpieces of art,

are still missing on the least of the Ministry of Culture

and Ministry of Foreign Affairs.

- Which is basically a cradle of civilization

when you think about it, right?

If you go through your average museum

and even the big spectacular ones,

and you count the number of artifacts,

it's dwarfed by what's been taken.

- [Narrator] It is nearly impossible

to estimate the full value of all that is missing,

but it would easily be in the billions today.

- [Piotr] So there is a lot of suspicion

that many of them may be still stored somewhere in the area.

- Are they somewhere in this tunnel complex?

- [Narrator] But is it more than just rumors leading experts

to think great treasures are lying hidden here?

Two dozen Renaissance portraits

were found in nearby Walbrzych,

and a chest of 103 silver objects

were discovered under the Nowy Sacz Castle,

to name just a few examples.

[dramatic music]

- And right to the very end,

at least some of them somehow imagined

that they'd survive all of this and, therefore,

wanted a kind of insurance policy.

- Well, the castle, the tunnels underneath

would've been the perfect place.

Nobody would've known what was under here.

- [Narrator] Evidence shows that one

of the most valuable historical collections

in the world was briefly stored here,

the priceless Prussian library.

It included original written scores by Bach,

Mozart, Beethoven, original manuscripts by Goethe,

as well as a Gutenberg Bible.

- The Prussian library was stored originally in the Berlin,

but because of the threat of the bombardment

and because of the threat it could be destroyed,

it was necessary to put it in a much, much more safer area.

So that's why it was evacuated to Lower Silesia

and stored for awhile in Castle Ksiaz as a safe place.

- This may have been a very opportune location

to stash all of this stolen loot they had taken.

You need somewhere to put those, [laughs]

so you're going to move them somewhere like Castle Ksiaz

because you have the perfect underground storage system.

- The looting was orchestrated and carried out by commanders

with directives from the top dogs,

guys like Himmler and Goring.

This is important enough that both the American Army

and the Soviet Army had specialized divisions of experts,

specialized units within their military,

whose job it was to try to trace some of the loot.

- [Narrator] Famously, the allies had the Monuments Men

who, throughout the war, went on dangerous missions

to recover lost masterpieces.

- They did find stuff in private residences.

They found it in museums. They found it in salt mines.

They found it all over the place.

- If you go to the Soviet Union,

there's stories about burying great works

of art in the gardens and covering them over

and to keep them out of German hands.

- And certainly that was done with an intent

that at the end of this, we need that art

to represent the survival of our people

and of the cultural historical legacies of our country.

- But no matter how heroically they tried

to defend some of these artifacts,

many of them were stolen and taken out of the Soviet Union.

- [Narrator] The tunnels under Castle Ksiaz

have only recently been open to the public and researchers.

However, not all the tunnels are accessible.

- And you can clearly see the shot leads up here,

but it's been completely blocked off.

It looks like it's been done deliberately

because there's way too much stuff here.

- [Narrator] As the Nazis retreated

near the end of World War II,

many of the were sealed off.

- The war's ending. Everybody knows it's over.

So why, as an SS commander, which you go to the trouble

and the expense, 'cause it took dynamite,

to seal all these tunnel off?

Well, there can only be one reason.

You don't want anyone to know what's in there,

and you want to come back to it when you're ready.

[dramatic music]

[car rumbles] [dramatic music]

- [Narrator] As the fates change for Nazi Germany

and the Red Army pushes towards the region,

the SS takes extreme steps to seal off the tunnels

and camouflage entrances to the caverns below Castle Ksiaz.

- The Nazis blew up and blocked off tunnels

when they eventually left the area.

Now, why would they do that?

Unless they had something really big to hide.

- [Narrator] It is thought that many looted riches

are buried in these tunnels.

But what exactly were the Nazis so eager to hide?

- If you're a senior Nazi at the end of the war

and you've managed to get your hands

on some loot or gold or valuables, wouldn't you want

to make sure it survived the enemy conquest,

maybe hidden away somewhere?

- [Piotr] The Lower Silesia

is an eastern province of Germany.

If you're losing the war, Germany haven't been expect

that they will lose this territory.

- [Narrator] However, after the war,

at the Soviet's insistence,

the region became part of Poland.

- After the war, so many masterpieces of art

had been found in the local palaces and castles.

So probably, they were sure indeed

that it was very safe place forever.

- [Narrator] Rumors abound about the fate

of the most famous artifact looted by the Nazis,

the Amber Room.

- the Amber Room is a symbol of looted art

which has been lost and never uncovered and never found,

a very mysterious case.

- [Narrator] It was assembled in Prussia

and given as a gift to Czar Peter the Great of Russia.

It measured over 590 square feet

and contained over six tons of amber.

- And then those thin pieces of amber

that they paneled the walls with

were all backed with gold leaf.

It must've been gleaming.

The room must've felt like you were sitting in the sun.

- [Narrator] It was installed in a permanent home

in the Catherine Palace and remained there

until it was dismantled and moved

by the Nazis during World War II.

Dubbed at the time the 8th wonder of the world, today,

its estimated worth is well over half a billion dollars.

In January 1945, Hitler ordered the movement

of looted possessions from the region.

- And completely disappeared.

Many treasure hunters, journalists,

and even secret services were searching for

and were looking for this masterpiece of art.

It's very famous, but it never was found.

- [Narrator] Could it be hidden away

in the tunnels underneath the castle?

- That's a good example of something

that continues to fascinate treasure hunters,

but also, there's plenty of Russians who work

in cultural institutions who would very much like

to recover some of these very important parts

of Russian heritage.

- [Seika] It was all put into crates.

Much like we move artifacts from Egypt

or anywhere else in the world

when you're shipping something.

- [Narrator] In October 2020,

Polish divers found the wreck of the SS Karlsruhe,

a ship which took part in Operation Hannibal,

a sea evacuation which allowed more

than a million German troops and civilians

from East Prussia to escape the advancing Soviet forces.

The wreck holds many cranes with unknown contents,

and some believe this may be the final resting place

of the Amber Room.

- What was the purpose of taking these kinds of artifacts?

What was to be done with them in the future?

And what purpose did they serve in the Third Reich?

- [Narrator] Much of the art loaded from Europe

was destined for the Fuhrer Museum,

a European cultural center planned

to be built in Hitler's hometown of Linz, Austria.

A massive model of the development

was created for Hitler by Hermann Giesler,

the architect of the Castle Ksiaz tunnels.

The museum was a grand project and not scheduled

to be completed for many, many years.

Thus, the Nazis had to find somewhere

to store all the looted art until it

could be moved into its permanent home.

- The Nazis envisioned themselves to be the defender

of European culture, not just of Germanic culture,

to entrench German culture and German nationhood

at the head of a European civilization.

- [Narrator] While we still don't know

if we will ever find the Amber Room,

there were rumors of another treasure looted

by the Nazis so valuable,

it makes the Amber Room seem small in comparison.

And as recently as 2015,

two treasure hunters claimed they had proof

that it was somewhere in one

of the lost tunnels near Castle Ksiaz.

[dramatic music]

A secret series of tunnels connected

to a Renaissance castle.

- One thing's very clear. [laughs]

They were interrupted in their building.

So what were their plans?

- [Narrator] As the Nazis retreat at the end of the war,

many of the tunnels are sealed up.

- Obviously, if you are doing that,

you probably have something to hide.

- [Narrator] Today, treasure hunters are still

in these hills in search of alluded treasures so vast,

it dazzles the mind.

- Stories of the Nazi gold train refuse to die,

and there are still people actively looking for it.

In fact, many are convinced that it's hidden somewhere

in a blocked off tunnel.

- This train was filled with what today

would probably be about a billion dollars worth of gold.

- We know that the Germans actually did hide treasures

in tunnels and that there had been treasure troves

of art found in odd places throughout the Reich

in the post-war period that there could be art

and treasure hidden in these places.

Why not a train?

- Original, the gold train story came

from the 70s where the ex miners from Walbrzych

have heard the story from his German colleague

who told him about the train with a load

of gold and other valuables,

which have been traveling from Wroclaw to Walbrzych.

It drive in into the tunnel and disappeared forever.

[dark brooding music]

- In 2015, two local enthusiasts finally put their hands up

and say, "We found the train.

We've been searching underneath and underground,

and we found some geological signs

that say that something's here."

- And they had a contact with Polish government,

and they announced that they found the gold train, actually.

- And they spent a lot of money,

and there was a lot of publicity

around their activities in trying to recover this train.

- The very high Polish officials said,

"We are sure for 99% that the gold train is down there,"

so everyone believe it.

- Well, all hell breaks out, controversy.

Everybody's arguing about

whether they finally found the train.

- And that's why so many people and so many media came here

and made it this huge story.

- [Patrick] The Polish Army come in,

but they say there's no sign of it.

- And in 2016 was a huge digging and drilling campaign,

but unfortunately, nobody found his gold train.

- By 2018, it became apparent that where they had hoped they

would find the train, the train was not there, and in fact,

one of the men dropped out of the project.

So there are still many who are hopeful

that there may be a train full of gold somewhere

in these tunnels near the castle.

But as of today, no such train has been found.

- We can safely assume that there's plenty

of treasure out there that we've yet to find.

There's plenty of secrets that we need to uncover,

and there's plenty of questions

that haven't been answered about these mountains.

Why did they build tunnels that this shape?

If this was simple storage places for munitions or food,

you wouldn't build them this way.

The tunnels are telling us

that there's something else out there.

- The tunnels seem like travel conduits.

They seem like a point of entry to get to somewhere else,

and the castle just happens to be the point of entry.

Where were those tunnels going?

What were they supposed to do? Who is traveling in them?

- The first thing I noticed when I looked

at the map of the tunnels is they're pointing outwards.

They're not interlinked, so in other words,

they must be built to go somewhere,

and we know that the Nazis had further plans

that they didn't get round to actually building

because the war ended.

So the question is what were they planning,

and how much of what they were planning do we know about,

and how much have we yet to find?

- Not far from the castle, there are a number

of enormous tunnel complexes over in the Owl Mountains.

This was known as Project Riese or Giant.

Now, is it possible that, at one point,

all these tunnels were, in fact, meant to be connected?

- [Patrick] This doesn't look like the same kind of rock.

Maybe they've got deeper into the mountain.

While we still don't have the evidence

to prove it one way or another, it's a theory

that more and more people are coming around to.

- It'd be a really ambitious undertaking to tunnel

from the castle over to the other facilities,

basically through Owl Mountain, a hard rock mountain.

It would take a really long time.

It would take massive amount of efforts.

There would be huge loss in terms of deaths,

but the Nazis were ambitious in their goals,

and I wouldn't put it past them.

- [Piotr] If we imagine that the finish

of this construction works at the Riese complexes

should be in the 50s, even,

there was enough time to connect it underground.

- We're still discovering additional tunnels,

additional facilities all the way to the present.

So there's still mysteries that are waiting

to be discovered.

And as an historian, you hesitate to say such things,

but the record is clear.

We continue with every passing year to find new evidence

of new Nazi tunnels, new Nazi facilities,

and this is so extensive under the castle

that I'm sure over the next few years,

they're gonna uncover even more tunnels

and more passageways that were unknown.

[birds chirp] [dark brooding music]

[dramatic suspenseful music]