Original subtitles

- This was a city underground.

- [Narrator] Five miles of tunnels buried 80 feet

below a small town in Austria.

- There's an interesting mystery here.

- It must have been housing something very secret.

- [Narrator] Here, in 1944, the Nazis set out

to build Hitler's newest wonder weapon.

- Nobody could imagine such a ferocious weapon.

- Leaps and bounds ahead of what the Allies were using.

- [Narrator] Decades later, historians wonder

if there was more buried here.

- What's there, what's Hitler got to hide?

- Some terrible things were happening in these tunnels.

- [Narrator] And an Austrian filmmaker's discovery

leads to new questions.

- The Nazi really hid it very well.

- [Narrator] But officials claim there's nothing there.

- Their sources have shut down any further investigations.

- Is the truth too dangerous to tell?

[dramatic instrumental music]

[tranquil string music]

- [Narrator] St. Georgen, Austria,

a little town just east of Linz,

the idyllic setting hides the dark truth

of one of the largest and

most mysterious underground compounds in the Nazi Empire.

- We love mysteries and conspiracies.

so the minute we see the entrance to these tunnels

we can't help but want to walk in

and find out a little bit more.

- Whenever you see a tunnel of this size,

this deep, underground,

it's almost inescapable you don't think what was happening.

And there's gotta be a secret.

- It's difficult to build.

It's a lot of effort, a lot of work, a lot of planning.

And that's interesting, I wanna know why did they do that.

- [Narrator] What secrets are buried

beneath these quiet hills?

- It's really amazing.

Some big structures!

Wow!

[urgent instrumental music]

- [Narrator] Bergkristall or Rock Crystal

is a grid of tunnels covering an area

of more than 530,000 square feet, 80 feet underground.

The original system was nearly five miles of tunnels.

But due to fear of collapse the majority

of the system was filled in

with concrete in the early 2000s.

There's now only about a mile of tunnel open.

But the tunnels of Bergkristall may only be part

of a larger mystery.

Austrian filmmaker Andreas Sulzer

has been researching the tunnels and the surrounding area.

- We have to cut this route to get in

with the heavy equipment.

And it took us a while to get in here.

It's my job as an investigative journalist

to do a good research and I think I'm not alone.

I'm part of an international group

with very experienced historians and military experts.

- [Narrator] Andreas has uncovered evidence

he claims points to something more.

- [Andreas] And they put a lot of effort

to hide it carefully.

- [Narrator] Government officials think otherwise.

- I offered them to make

an international research consortium.

They always refused.

Why, what's the reason?

What's the problem to work with experts, internationally?

There must have been something more than officially known.

- All governments have a duty to protect their citizens,

and sometimes that means withholding information.

So, the question is here.

Are we talking about a situation

in which authorities believe

that the truth is too important

or too dangerous to tell?

[urgent string music]

- [Narrator] Bergkristall is the only

officially acknowledged tunnel system in the area.

- I can't imagine building a tunnel

of that size underground, and as quickly as they did,

and reinforcing it as much.

- [Narrator] The Germans hired Viennese engineer

Karl Emil Franz Fiebinger to design Bergkristall.

- The nature of this ground lent itself

to very efficient tunneling.

They didn't need a tunneling shield,

which is a complex piece of machinery.

They didn't need to blast their way through.

And so, they were able to make fairly quick progress.

- It's pretty astounding.

There's constraints here that we don't have

when we're working on the surface.

You can only fit so many workers in one space.

You can only operate so much machinery in one space.

- Whilst these tunnels may have been dug quickly,

they were designed and built well.

They were designed to last.

- [Narrator] Fiebinger was known

for his underground engineering.

And after the war was brought to America

as part of Operation Paperclip.

- Operation Paperclip by the Allies prioritized grabbing

as many Nazi scientists, engineers, technology,

and systems as possible,

and whisking them back to the United States.

- [Narrator] What could've been the purpose

of such a vast network of tunnels so far underground?

- With these tunnels there are so many questions

as soon as you look at it

that just beg to be asked?

- It must have been housing something, something big.

Probably extremely dangerous.

Something that you wanted to keep very, very well hidden.

- We do know that diabolical military research

was being done in the tunnels.

- So, Bergkristall would be a

very juicy target to hit, indeed,

if you knew where it was.

- [Narrator] Andreas believes there's more to this place

than what's in the official records.

He made a surprising discovery

while investigating a former SS Rifle Range.

- Yeah, here it is, you see?

Is it here? - Yeah.

Oh yeah, here's the next one.

So, this here was the original soil level.

And we had to cut through with the Caterpillar.

And for our surprise, here,

we found hard steel

and it's a tank barrier out of steel, those crosses.

So, this is a very important find,

because on a normal rifle range

you never would have in the middle of the shooting line

a tank barrier.

This was the first hint that here must be something

in the deeper ground.

- There must be more here.

- [Narrator] A tank barrier would only be installed

to keep invaders out.

What were the Nazis trying to secure here?

And why did authorities cover it up with tons of soil?

- You see the level?

The ground level here is higher than the level here.

- And the Nazis hid it very well putting all this soil.

So, you can imagine how much work this is

to fill up this soil in here to hide it.

It's unbelievable.

- Andreas is not just digging

into the earth of these tunnels.

He's also digging into the accepted history

as we understand it, of the Second World War.

[tense instrumental music]

Austria is incredibly important to Germany in World War II.

For Hitler, it was a sign of his divinity that he was born

on the exact border between the two countries.

It meant that annexing that country, taking it over,

making it integral to his Reich was a part of his destiny.

- There were Nazis within Austria

that were trying to overthrow the government,

push the government to welcome the Germans.

And, finally, on March 12th, 1938, it happens.

Austria is annexed.

And Hitler gobbles up Austria

basically without a shot being fired.

Austria offers the German people

not only territory next to Germany but natural resources,

it's a natural resource-rich country, and skilled labor.

Some of the leading scientists at the time were Austrian.

[unsettling string music]

- [Narrator] Following the annexation of Austria,

slave labor was brought in

to build Mauthausen Concentration Camp.

The camp was located near a granite quarry 12 miles east

of the city of Linz.

And, today, is one of the most visited by tourists.

- All the concentration camps were unimaginably horrific,

but Mauthausen was one of the worst.

It was one of the first.

It was one of the largest.

And it was one of the most deadly.

Mauthausen had tens of thousands of prisoners in it.

We don't have an accurate count

of how many died in Mauthausen,

but the numbers that are given are anywhere

from 125,000 to, perhaps, 320,000.

Mauthausen had people from all over Europe.

There were Jews there.

There were soldiers.

There were intellectuals.

But it also had a skilled labor force.

- [Narrator] Nearby, yet strangely forgotten,

were the Gusen subcamps.

[dissonant string music]

- This is the Gusen River.

We are inside the concentration camp now.

- [Narrator] Prisoners from these camps

provided slave labor for construction projects

undertaken by the Reich.

- We are here, now, standing in front

of the so-called Schleppbahnbrucke Bridge.

A bridge that was designed

by the SS of St. Georgen and Gusen,

and constructed by inmates of concentration camp Gusen

in only one day and one night.

- Even with the forced labor

that they had available to them,

it's an engineering feat however they did it,

if they did do it in such a short period of time.

- [Rudolph] This bridge was constructed

to link Gusen Concentration Camp

with the river system of the Third Reich.

Over this bridge all the material

of the concentration camp, even transfers of inmates,

were sent also from other concentration camp

into Gusen via this facility.

- [Narrator] Why were the Germans

building up the Gusen area so quickly?

And why the rounding up of highly skilled

and technical labor?

- Ah, yes, you could see it here.

- Here we are.

- [Narrator] Back at the rifle range,

Andreas makes another discovery

that leads to even more questions.

- It's much too massive and too high

for a shooting range.

- [Narrator] Who buried it and why?

And why did authorities stop him from digging?

- They immediately stopped

all further investigations on the spot.

- So, the authorities say one thing,

but Andreas has a complete different theory.

Who's correct?

[suspenseful instrumental music]

- [Narrator] World War II, Bergkristall was a network

of tunnels covering over 530,000 square feet

under the hills of St. Georgen, Austria.

- One of the largest underground facilities ever built.

- [Narrator] The tunnels were dug in just over a year

by thousands of slave workers

from a nearby concentration camp.

Seven decades later, documentary filmmaker Andreas Sulzer

has made a surprising discovery.

- I think we are very close.

It's here on top here.

- [Narrator] Andreas found a tank barrier

buried 16 feet underground at an old SS Rifle Range.

- Why, why to build any barrier here?

- [Narrator] He made this discovery

while investigating another strange clue he'd found

at the rifle range.

- We found a very detailed supply intelligence report

of an informant

who gave an exact location

north of the known Bergkristall for an underground entrance.

One kilometer north of St. Georgen after the road

is an SS Rifle Range.

And just north of it is a mountain

where a large excavation has been made.

Excavation is about 200 square meters.

[intense instrumental music]

So, here is the Bergkristall entrance.

So, here, is the rifle range.

And then he says, just north of Edtsdorf and running

in a north-westerly direction is a low range of hills.

For a distance of about 3 kilometers

numerous excavations have been made.

And that's all before Bergkristall was built.

- [Narrator] After excavating 16 feet deep,

they made a discovery.

- We found a concrete plate.

And then we found a stair.

[clock ticking]

- There's an interesting mystery here.

- The stair always leads to something.

- What's there?

What's Hitler got to hide?

- [Stephan] And then we digged, and digged,

and digged down there.

- [Andreas] Yeah, and then you go for the next stair

and for the next stair.

Crazy, absolutely. - And for the next stair.

- So, also, the structures you see here.

These really good made structures.

- [Andreas] So, it's a very strong building here.

- It seems like every passing year

since the war has ended,

people are finding new Nazi tunnels,

new Nazi trenches, new Nazi bunkers.

I mean, just remarkable.

- And here was a kind of a generator built in,

because here is a tank.

It's a tank, it's a full container for a generator.

And here we ended up.

We were stopped by the authorities, by the police.

Suddenly, one day before Christmas

the police came and stopped the whole excavation.

Within two weeks,

the whole property of the SS Rifle Range

was immediately put under cultural heritage.

No digging, no excavations,

no analysis.

And Bergkristall was set

under cultural heritage months later.

- [Narrator] Why would there there be secret tunnel entrance

buried in the back of a rifle range?

Why have the authorities gone to such effort

to stop Andreas from investigating, even at Bergkristall?

[intense instrumental music]

Construction work for the tunnels began in early 1944,

and would be continuous

until the area's liberation in May of 1945.

But why was it built?

- By 1944, it's clear to anyone who is sane

that Germany is losing the war.

Surely, there can be no hope for the Third Reich.

The Allies have got complete aerial dominance,

which means that they can attack almost at will.

And the Luftwaffe, the German Air Force,

almost aren't able to put up any kind of resistance.

- We do know that some terrible things

were happening in these tunnels.

None of that is conclusive,

and it's not open for discussion.

That's the Messerschmitt Me 262.

- The Messerschmitt 262 was

the world's first jet fighter plane.

And it was a game changer for the Germans,

because the Allied planes at the time

were all propeller-driven.

These jet propulsion planes could pass

all of these propeller planes in the air.

- [Narrator] The Me 262 could fly 93 miles per hour faster

than any Allied fighter plane,

up to 530 miles per hour.

And a jet could hold its speed in turns

much better than a propeller-driven plane.

- By now the Allied pilots have become

so accustomed to dominance in the air,

that the Me 262 when it arrives in the skies

blows them apart, quite literally.

They've never seen anything like it.

The fighter flies past them

and tears into the bombers.

- Nobody could imagine such a ferocious weapon.

They had a fighter version known as the Swallow.

They had a fighter bomber version knows as the Storm Bird.

The Nazis had claimed just at the end of the war

that these two types of Me 262s,

that they shot down 550 Allied craft.

Imagine if they had brought those

on line in 1940, '41, or '42.

- Having the world's first jet fighter on your side

is a huge leap in technology.

They would be so much more effective

than anything else in the skies at that time.

But if this was gonna play to Hitler's advantage,

he needed to get those planes up in the sky

winning the air battle as quickly as possible.

- [Narrator] The airplanes were built entirely underground

on assembly lines nearly a mile long.

- Why would you manufacture a plane in such conditions

when you could have manufactured it above ground?

- The only thing I can really thing of is protection,

protection from bombing, and the ability

to just continue to work without interruption that way.

- Clearly, you're delaying any kind of project

when you decide to bury it underground.

You only do this for projects

of critical and national importance.

And it's hard to imagine a project more important

for the Nazi war military machine

than the development of the first ever jet fighter.

- In order to achieve

this underground production facility.

I mean, they were basically building

an aircraft factory underground.

They had to tunnel out on a scale

that they'd never done before.

- [Narrator] The Bergkristall plans called

for 19 main tunnels and nine cross tunnels at right angles.

Each tunnel was 15.4 feet high,

and reinforced with concrete on the walls and ceiling.

- The workers would dig vertical shafts with shovels,

and then use air hammers to blast

their way through the ground, outwards.

The earth would be loaded onto huge conveyor belts,

which would move the soil away from the tunnels.

It was then loaded onto carts and wagons to be taken away.

- As soon as they built these tunnels

they needed to build cribbing and shoring

to create structure to maintain the shape of these tunnels.

That was likely done by using timber,

and later installing a concrete shower.

They would also put a concrete floor on.

- And Hitler demanded

that this facility would be up and running

within a year of them breaking ground.

From an engineering perspective,

that's giving you one big headache.

- [Narrator] It would take 3,000 prisoners

working 8 to 12 hour shifts almost a year

to carve out this space beneath the earth.

- This facility had its own septic sewage treatment.

It had its own heating, ventilation, and air conditioning.

- Any testing of these planes

would have generated large amounts of exhaust

within these tunnels,

which would have rendered the air quality very poor,

and made it extremely difficult to breathe.

- The underground tunnels, they're like a city in a city.

It's almost like an ant heap.

There's a huge amount of activity.

And it's all working together to produce planes.

- I can't imagine building not just an airplane in that

but a brand-new type of warplane that's jet-powered.

And then on top of all of that

bringing it up and launching these things,

it boggles the mind.

- Do you build it in pieces?

Do you build the fuselage separately from the wings?

And then do you put that together outside?

The logistics of it just become significantly more onerous.

[unsettling instrumental music]

- [Narrator] Despite all the complexities,

German records have the tunnels finished

and the jet fighter assembly line

up and running by March, 1945.

[urgent piano music]

At the height of production,

there were a rumored 11,000 slaves

working underground at Bergkristall.

- These were prisoners of war, were foreign workers.

These are the people that would have been responsible

for building these planes,

and many would have died in the process.

- [Narrator] Only two months after its start,

the jet production was stopped

in anticipation of the Allies' push into Austria.

By then the plant had already built nearly 1,000 planes.

But why is the existence of other nearby tunnels in dispute?

- What's interesting is that

the jet plane production was already decided.

So, we speak about two different productions, maybe.

What's the question text for?

- [Narrator] What secret new terror

were the Germans building in the tunnels

beneath the Austrian countryside?

[suspenseful instrumental music]

1944, the war has not been going well for Germany.

And the Nazis are desperate for an edge,

something that will turn the tide of the war in their favor.

- By now swarms of Allied bombers are hitting German,

military, industrial, civilian targets.

Anything that makes anything, moves anything,

they're gonna bomb it.

The Germans need to come up with an answer.

- [Narrator] The Nazis approve plans

for a 530,000 square foot complex

buried deep beneath St. Georgen, 10 miles east of Linz.

Filmmaker Andreas Sulzer's recent findings in the area

raised questions that authorities dispute.

Could the tunnels extend farther than Bergkristall?

- This is also very interesting,

because here is also the stone wall.

And here is a plate on that stone wall.

So, if this will be the end,

here will be a concrete fundament.

But this is definitely a wall.

Same thickness like that,

so there is something beyond this wall.

- What do you think the stairs goes down, again?

- It's also possible that it turns here

in the middle somewhere, again.

An angle to get down.

It looks like a-- - A small platform

then it goes right, then, maybe, down to here.

- We're already deep down here.

So, it's up where is the starting point.

It's eight meters.

- [Stephan] Yeah, I think so.

- That's unbelievable and it's not the end.

- It's not the end, no.

- But we were forced to leave the excavation site.

Everything is forbidden here now, yeah?

- [Stephan] Yes.

[unsettling string music]

- Related to Bergkristall, of course, is Mauthausen,

but much more related to Bergkristall

are the Gusen Concentration Camp.

- [Narrator] While Mauthausen is one of the

most visited by tourists, the nearby Gusen Camps

were completely forgotten until recently.

- I started more than 30 years ago

to research on that lost history of Gusen,

because nobody didn't know anything here in Austria.

- I'm born here in Linz.

I went to the school.

I studied here, but I first heard in my life

with 45 years

that Gusen existed.

I never read about that before.

[somber instrumental music]

- So, Mauthausen was not only a large concentration camp,

it was massive because it had approximately 100 subcamps

or satellite camps stretching

across a vast territory.

Perhaps, the largest of Mauthausen's subcamps was Gusen II.

And Gusen II was particularly bloody and gruesome.

In 1942, so many prisoners were dying

that Gusen II builds their first crematoria

to start burning all the bodies.

- When we talk about Gusen,

we talk about an unknown camp,

a still kind of secret camp.

Why is Gusen not known to the public

or to a wider community?

- [Narrator] After the war, most of the camp

was destroyed by the occupying Soviets.

They didn't want to commemorate a place

where so many of their people

had been imprisoned and killed.

- In 1947,

the Soviets even placed 54 bombs

inside the tunnels of Bergkristall.

So, it almost collapsed after this big explosion.

And, therefore, Gusen was forgotten.

And the Republic of Austria did nothing after the Soviets.

- Gusen, more or less, was a death camp.

There are nearly no survivors.

Nobody could speak about the situation here.

- [Narrator] Could there be a connection

between the forgotten camps of Gusen

and the mysteries in the tunnels?

- But Gusen was not only a concentration or a death camp,

it was also a high-tech

industrial park of the SS.

The longer the work got,

the importance of Gusen increased, increased, and increased.

- From mid-1944

the SS starts

to pick skilled workers under the prisoners.

For example, miners for underground building

and sent them over here to Gusen.

And in the later course of the war,

you see that they select physicists and chemists.

They must work on some special projects.

- [Narrator] Why were some of the most

highly skilled prisoners being brought in from camps

to work in the area?

[airplane engine roaring]

As the tide of the war turned,

Hitler relied more and more on wonder weapons,

technological breakthroughs

that he believed would give the Nazis a much needed edge.

- The Nazis made impressive progress

on these terrifying weapon systems.

The V-2 rockets, they were working on a V-4.

These things were just state of the art,

futuristic weapons of terror.

- [Patrick] If you look at the Nebelwerfer,

which is the multiple rocket launching device

strikes fear in the Russian troops they fought against.

And it's leading technology.

- Surely, there's some wonder weapons we don't know about.

A lot of their most impressive weapon systems are coming

on line right at the end of the war.

- Propaganda is promising this to the German people.

These Wunderwaffe, they're coming, they're wonder weapons.

So, the German engineers and scientists need to deliver.

Is the wonder weapons gonna be able

to get them out of this disaster

that they created for themselves?

- [Narrator] Could the other tunnels nearby have been built

for another one of Hitler's secret weapons?

- It's almost as if they believed they're gonna win the war,

perhaps, with what they're building in these tunnels.

- [Narrator] Seven decades after the end of the war,

Andreas has discovered something in the tunnels

that set alarm bells ringing for his team.

- Was there something more happening down there

than just the assembly, the Messerschmitt 262?

- [Narrator] May 7th, 1945,

the Allies arrived at Bergkristall,

a massive underground factory

where Germans had been building

the world's first jet engine plane, the Messerschmitt 262,

only to discover its secrets destroyed and buried.

- All of the sudden there's a new type of flying vehicle

that blows by them at speeds

that they thought were logistically impossible.

- [Narrator] Seven decades later,

new discoveries prompt some to wonder

if the tunnels run deeper than anyone suspected?

- A lot of what the investigation is finding down there is

certainly opening up unanswered questions.

- [Narrator] Documentary filmmaker Andreas Sulzer believes

there's more than just Bergkristall.

His excavation at a nearby rifle range has provided him

with some clues.

- Before we started excavating there,

we made a geoelectric on top of the hill

of the rifle range.

If you go further into the hill

where it rises up, you see this structure inside.

And that's the resistance of air and concrete here around,

so there's inside the hill.

- Two underground? - Yeah.

It's huge structure in that hill.

But the Allies, it looks from the air

likes it's just a simple shooting range.

But in my opinion

and based on the other things we found here,

it's a very good camouflage entrance

into underground facility here.

That would be really, really interesting

to excavate all here.

I can't face it why the authorities don't want to dig here.

It's what's so important to find out

what's inside here in the hill.

And there is something in there.

- [Narrator] Though much lies in rubble,

Andreas has discovered a curious clue deep

within the tunnels of Bergkristall.

- When I was in the Bergkristall Tunnels, first time,

I had a Geiger counter with me.

It's normal when I enter underground facility.

You never know.

We saw 2.6, 2.8 microsieverts per hour,

which is 20 time higher than the normal.

- Andreas is claiming that the radiation levels

he measured when he went down into these tunnels

is far higher than anything

that would normally, naturally occur in geology.

- [Narrator] In January of 2015,

historians at Mauthausen-Gusen convened a panel

to address the ration question.

- The Austrian authorities are very clear.

They say that the radiation is natural.

It comes from the rocks and the surroundings.

- Radiation can come strictly from natural surroundings.

However, the radiation levels

that Andreas would have found

are suspect, especially if we do not know

what this official source of radiation is.

- [Narrator] Whatever the source, the radiation levels

are high enough that the tunnels

are closed to the public 362 days a year.

- Well, these tunnels are open

for a very brief period of time.

They require scrubbing basically to clean the environment

of radioactive materials.

That's a huge undertaking to do and very expensive as well.

- [Narrator] So, where is this radiation coming from?

Is it purely natural?

Andreas has other darker theories.

- In the course of the war

when the SS got more power,

they moved in also top secret projects

under the wings of SS General Hans Kammler.

He was one of the most powerful, high-ranking SS generals.

When the Allies attacked Peenemunde,

the famous Peenemunde rocket production,

Hitler ordered Kammler to move all the rocket

and wonder weapon production underground.

And Kammler was responsible for that.

- [Narrator] Andreas believes that Kammler

may have had an atomic weapons facility

built in secret tunnels beneath Gusen.

- He erected hundreds of underground facilities,

partly in old mines,

but also with new underground buildings.

One thing is quite clear,

Kammler shows up very early

in the area of St. Georgen and Gusen.

And this has nothing to do with Messerschmitt.

This has to do with his SS secret weapon production.

So, there must be something else.

[suspenseful instrumental music]

- [Narrator] Why have the authorities

stopped Andreas from investigating?

- The Americans had some hints

that there must be here also underground facilities.

- It's really amazing.

- [Narrator] Could the tunneling have been

much larger than just Bergkristall?

[urgent instrumental music]

In the span of just over a year,

over 530,000 square feet of tunnels had been dug

near the small town of St. Georgen, Austria

by thousands of slave workers

from nearby concentration camp Gusen II,

which until recently was all but forgotten.

In these tunnels the Germans would set out

to build fuselages for the first jet engine aircraft

they hoped would turn the tide of the war.

- While this miraculous underground machine is happening,

building these planes, you've got these auxiliary tunnels

that are nearby that we don't even know

the extent of them yet.

- [Narrator] Filmmaker Andreas Sulzer believes

that the entrance he found is part

of a secret tunnel system codenamed Esh-shay.

- Esh-shay was a project by organization Todt

also involving the deaths and the SS

for underground production to St. Georgen, Gusen.

You see here at the rifle range.

You see here a huge structure

on top of the hill.

And also here are shafts.

So, that's in here, that's the area.

We excavated this entrance.

So, when we go a little north

at the workhouses for Esh-shay.

And here lived, based on other documents,

German engineers, workers for the Esh-shay.

So, this is already proof that Esh-shay was realized.

And we also have other documents.

But what is really, really interesting

that the Americans tried to bomb this area.

So, you see very close by--

- Intensive bombing.

- Intensive bombings.

You see here the bomb craters

which are partly filled up, again.

But the Americans had some hints

that there must be here

close in that area also underground facilities.

- These are things that people are working on.

They're not meant to be found out.

So, it shouldn't be surprising for us

that we still have things to find out

about what these men were doing in these tunnels.

- Okay, let's have a look.

- [Narrator] Andreas and Stephen

have explored testing tunnels

they believe are part of the Esh-shay system.

- These tunnels were setup and built in autumn 1943

onwards to 1944

in order to test the stability of tunnel systems.

So, they built different tunnels in different depth

of the sandstone.

And they exploded on top of the hill different bombs

in order to simulate if the tunnels would break in.

When we, first time, went in the test tunnel Esh-shay.

So, after some hundred meter it goes deep down.

- It's really amazing.

- [Andreas] And it's broken in from the explosion,

so it's not possible to go further.

- They dropped the bombs from outside

and the structure was broken.

- And, of course, it's very dangerous going

in here, down deep, because when you are close

to the breaking point,

you can feel while walking

that beneath your feet is another tunnel.

So, the ground starts to vibrate.

It's really dangerous to go in there.

It's a very dark,

scary place.

It was made by hand with picks

by the prisoners, so you see the scratches.

It's quite possible that from here

directly underground is a connecting tunnel

to the underground facilities in St. Georgen.

- I think you could go down and down here.

It's really amazing.

It's so big.

- They made, I think, three to four tests,

but the really interesting thing is

there's a testimony from a survivor, prisoner,

who attended the last test.

And the last test was a bomb underground in the tunnel.

Prisoners and sheep were brought

into the tunnels underground close by the explosion space.

- I heard from local eyewitnesses

that when the detonations were done

that they have seen mushroom clouds went into the sky

already in March or April, 1944.

And even three, four kilometers away of the detonation point

the roofs of the farmhouses were damaged,

all the windows were damaged.

This was not an-- - This particular air

is from a shockwave.

- [Rudolf] It was not an ordinary explosive.

- And after that explosion, a special commission came

and the whole area was shielded.

Nobody was allowed to enter.

And we found that on the same day

when the commission came,

Wernher von Braun is flying to Lintz

in his one day on a secret mission.

- [Narrator] Wernher von Braun was Germany's

top rocket scientist later captured by the Americans

to work on the Space Race.

Why would he be conducting secret

and urgent site visits to this region?

What else was being created in the tunnels here?

- This is a very, very, very threatening truth.

- [Narrator] Is there an atomic facility

buried here at St. Georgen?

And if so, how close did the Nazis come

to making such a weapon?

- Could the whole war have been completely different?

[unsettling instrumental music]

- [Narrator] In the aftermath of World War II,

the Allies liberated one of the largest concentration camps

in all of Europe and destroyed tunnels at Bergkristall,

a massive underground aircraft factory.

Seven decades later, evidence of radiation

has some investigating

whether there was more going on in these tunnels

than officially reported.

- Officially, there's only Bergkristall.

But we see in the documents and evidence we have

that there is a complex of underground system.

They dug about eight underground facilities in the area.

[urgent instrumental music]

- [Narrator] Andreas found a report

from the American General George McDonald,

a military intelligence chief, after the war.

- He visited personally underground facilities

which were in size from five to 26 kilometers.

So, we involved military experts who proofed

all the aerial reconnaissance and the reports.

Is it plausible?

So, you can see the excavation spots

where the Nazi moved the spoil

from the underground excavation.

And our experts did calculations on that

based on the size of the tunnel.

We are talking about 40 to 50 kilometers

in total in that area.

And officially known is six or seven kilometers.

- [Narrator] But Andreas found another

even more fascinating note in McDonald's report.

- That's an interesting point, certain.

It was recommended that this paper be forwarded

to headquarters Army Air Forces with the idea

of selecting targets of above mentioned types,

this refers to the underground facilities

mentioned or inspected,

for secret experiment of rocket-propelled atomic bomb.

- Building an atomic bomb, a nuclear device,

is extraordinarily complicated,

especially for the '30s and '40s.

Remember, the Nazis are on the cutting-edge,

and they're just beginning to develop jet-powered planes.

They're just beginning to develop rockets.

So, the idea of an atomic bomb.

This was futuristic.

- We know that the Nazis were looking at atomic energy.

They understood the principle.

The scientists go to Hitler,

and they present to him a roadmap

for how it could be achieved.

But there is worries just about anyone else

about what Hitler can do with this.

And so, they actively try and dampen down his enthusiasm.

Hitler goes along with them,

and he doesn't make creating atomic weaponry a priority

for the Nazi Reich.

But that doesn't mean

that the Nazis stopped any investigation,

any scientific work, into nuclear development.

On the contrary, in 1942,

they created what was known as the Second Uranverein.

This project dedicated to atomic bomb creation.

[tense instrumental music]

- [Narrator] But what does it take to build

such an atomic weapon?

- You need to build a particle accelerator

to fire neutrons at atoms

to split the atom, which releases energy,

which causes a chain reaction

where other neutrons split more atoms,

and that atomic explosion, that explosion of energy happens.

[dissonant instrumental music]

- Before the rifle range was excavated,

we had another spot where they said, "There is nothing."

- [Narrator] Andreas's team found

a 98-foot, sealed, concrete octagon.

- In the aerial photographs we see that octagon.

During World War II it's open.

But the SS sealed it some weeks before the Americans arrived

and hid it with soil.

- [Narrator] During the excavation Andreas

found an artifact that might've given a clue

to the atomic question.

- It was a ceramic roll.

And it's part of a particle accelerator.

We have original photographs of this type,

which is from 1943, the same piece.

And we sent those pictures to physics institutes.

And they also kept the confirmation

that this is part of a particle accelerator.

- [Narrator] But Austrian authorities disagree.

- They say it's a part of a motor.

It's a wheel for a motor,

but it's definitely not because it's ceramic

and it's very fragile.

And even the metal rings are very, very thin.

- [Narrator] One week later,

the authorities stop the excavation.

- So, the octagon

was immediately covered again with soil.

So, it's, again, away from the site.

- [Narrator] Did the Germans

have the resources to build this?

- To have access to that type of technology,

and the space that something like that would've taken,

I'm just not sure if it would've been possible

to do something like that underground.

- This is not off-the-shelf science.

This is specific, it's expensive.

It's energy intense.

- [Narrator] The energy from an atomic bomb

is released as both heat and radiation.

Could this be the source of radiation

lingering at Bergkristall?

- Officials claim that any radiation detected

in this area is coming from the ground naturally.

And that does occur in geology.

There's nothing strange about that.

Another theory is that this radiation

is coming from man-made atomic programs.

Which is true, we may never know.

[resolute instrumental music]

- It's hard to believe that Hitler

wouldn't wanna pursue the power in the atom.

He's power hungry.

Why wouldn't you pursue that avenue?

- If there was just a hint of a suggestion

that these tunnels were part

of a secret Nazi atomic bomb creation project,

then the Allies would've stopped at nothing

to get inside the tunnels.

- So, is it possible

there was some sort of atomic research going on

at Gusen II or Bergkristall,

and the Allies grabbed it and took it back?

Yes, it's possible.

We don't have any evidence for it.

- One thing is for certain.

Had the Nazis got their hands on nuclear capabilities,

[sighing]

the thought of that is absolutely terrifying.

- I think if Hitler had an atomic bomb,

he wouldn't have hesitated to use it

to end the war to his advantage.

And I also think he wouldn't have hesitated

to use it even if he knew he was going to lose.

He's going to go out swinging.

To hell with anyone.

- It's shocking for me not to be interested

to uncover the truth.

We owe it to the victims and to the families.

And I think also it's very important

for people who live here or want to build a house

to know what's under your feet.

- Some people are obsessed with finding the truth,

and they do that for personal reasons.

Sometimes, they have a greater mission

that they're working towards.

But if we can understand what happened

in this particular period of time,

which more than any other conflict

has created the world we live in today,

then I think that's gonna be a good thing for us.

- [Narrator] As experts continue to struggle

to find answers hidden in the hills of St. Georgen,

we can only imagine how far the Nazis got

in their atomic research,

and how many of their secrets are still buried here.

[urgent instrumental music]