Original subtitles

Hidden Worlds 3D - Caves of the Dead

Yucatan, a peninsula on the land bridge between North and South America.

The heartland of the historical Mayan empire.

Ostensibly, an arid coastal region without rivers or large lakes.

But numerous, mysterious waterholes in the middle of the jungle

tell a different story: of a secret, hidden beneath the surface.

Trees and plants stretch their roots here, in the dark kingdom

of three subterranean rivers - Yucatan's lifeblood.

They flow through the presumably largest underwater cave system on earth

extending beneath the peninsula.

Formed for millennia, accessible only through crevices in the limestone rocks

and shrouded in mystery - the cenotes.

Even larger quantities of rain rapidly seep through

the porous limestone, creating a dry and almost inhospitable effect.

Yet the subterranean water resources

ensured and still do provide lush and varied vegetation.

The Maya often built their temples close to the cenotes,

as in addition to providing their water supply, they were considered to be the sacred entrances to Xibalba:

the Underworld - the mysterious realm of darkness, of fear,

of death - ruled by the gods.

The appeasement of these gods constituted a special place

in the rites and ceremonies of the Maya.

Long before the first Europeans set foot on the American continent,

trade, science and social life

flourished in Yucatan.

Divided into city-states, based on strict, religious rituals,

the Mayan Kings ruled their empires unrestrictedly and as equals with their gods.

Numerous mysteries revolve

around the history of the Central American continents

most significant civilisation.

The ballgame of Pok ta Pok is closely associated with the myth of Xibalba.

It was based on an ancient legend,

in which the battle between the twins Hunahpuh and Xbalanque is re-enacted.

They descended to Xibalba,

where they were challenged by the gods to play a ballgame.

According to legend, they defeated the gods of the underworld

and ascended to heaven as the sun and the moon.

The game was also seen as a symbol of the cycle of life, mankind's journey from birth to death.

However, death was very real. The captain of the victorious team team was sacrificed

to the gods of Xibalba and thus acquired godlike status. A bloody custom, but also a

great honour apparently, which was hard fought for.

Now, little more than crumbling stone buildings testifies to the former power

and progress of the Maya Kingdom.

Here we have Robbie Schmittner and Florian Huber.

The former is one of the most experienced cave divers of the region.

Florian is a marine archaeologist from the University of Kiel in Germany.

Both are united in their fascination for the ancient relics

that can still be found in and around the cenotes.

For several years now, Florian has been commuting to Mexico with

a team of research divers of the Kiel Institute of Prehistory and Early History.

The Yucatan primeval forest is yet to reveal all of the secrets of the Mayas.

Treasures, hidden in the dense jungle

and the subterranean rivers and cave systems of the peninsula.

Robbie Schmittner's diving centre in Tulum.

The linchpin for exploring Yucatans underwater world.

This gives us an insight. What we just saw on the big map

is just a system of around 200. When we take a look

at what we have in this system, we can see 3 main arms. This one comes down

that one there and this one comes down here.

That's why this system was called Os-Bel-Ha,

which means three waterways. They're partially connected

at the sides, but the main passages are OK.

At some point, sometimes indirectly, the water eventually manages to run out to sea.

Florian Huber, Robert Lehmann, Christian Howe

and Uli Kunz have spent the past four years

exploring the Yucatan cave system. A highly-specialised team of professionals

who meticulously plan every dive they make.

Always, unfortunately. You know, whenever real characters have to work together,

there's always friction. Since 1980, most researchers

who've been exploring here gave their data to QRSS, a base

where all data is stored and they reach a point where sometimes something gets lost

or someone doesn't pull his weight. It could be that something's missing here or there,

but most of what's been found so far can be seen on the maps.

We want to risk it and dare to undertake the journey into the mystical underworld

of Xibalba, which, in the days of the Maya, really was a journey of no return.

Today, it is one of the biggest big challenges a diver can face.

But before the scary stuff starts, we still have some humping to do.

Before each dive, about a ton of equipment has to be loaded.

At 30 degrees in the shade, this is a challenge for any deodorant.

Then we're off, at first, through rough terrain

in the middle of the Mexican jungle.

En route, we have to make our way through the dense forest with a machete.

Florians GPS shows us the way.

Flo, what does the GPS say? Where are we going?

This way I think. - Here? OK?

I think I see water over there.

Oh wow, look, clear water.

Now, that is a hole.

It's a good sign to see fish here.

In every cenote we find with a cave beneath it,

we nearly always find fish.

There's an awful lot of organic material in there

that first has to be chopped out.

Someone has to go in with a mask and see if there's a tunnel.

It's best Rob goes.

Hey, here is something.

Robbie, I can feel stone here.

If you look, there's a crevice in the middle.

It's improbable that the cave ends in the middle.

Look at the side. Over here.

Oh man, where is he?

He's OK.

Fantastic.

It's a really great cave.

It drops down a lot here at the front, but there's a really small fissure.

You have roughly four metres, then you have to submerge.

Once you get through there's a small fissure.

We can get through sidemount, so you can forget backmount,

we need complete sidemount equipment.

You'll probably have to take the bottles through up front,

it's really narrow. But then the cave just opens up really big, it's beautiful.

So we're off, we've discovered a cave opening.

But first we have to hump all of the equipment over here

and set up a safe base for our first cave dive.

While the team is getting ready,

Robbie looks for the best place to attach the guide rope.

We need that to find our way back out again.

Oh no, it stinks here SO bad.

That's us.

Yes, when you come out again maybe.

That'll be quite something. Robbie, take a deep breath.

Nice.

Man, it stinks to high heaven here.

Ok, let's go! You follow us.

We descend through a dense forest of reeds and underwater plants.

Some of the plants almost seem to breathe in the light of our lamps:

A surreal sight, which complements our descent into the underworld.

We find the passage one after another and carefully dive through.

Now, we are entering Xibalba, the caves of the dead.

The safety rope will guide us back again.

I hope. it's vital to secure it properly,

as it's easy to get lost in this labyrinth of caves.

That could end badly,

as down here it's impossible to surface quickly for air.

The cave narrows, we carefully continue our dive...

The first obstacle: A very tight section that we can only get through

with the scuba tank stretched out in front of us, a so-called twister restriction.

Time to take off the equipment and pull our stomachs in.

The name twister restriction comes from the style you need

to adopt to pass through. The only chance you have of coping with bottlenecks

like this is to turn, little by little, like a screwdriver.

At the same time, you have to fight against the current.

On top of this, the dispersed sediment hardly helps matters:

within the shortest space of time, vision is down to zero.

This is definitely not for the faint of heart. Just what have I got myself into?

Ah well, made it! I ask myself if I'm the only one

feeling a little queasy in this pitch darkness.

Well, not Robbie anyway. He calmly secures a marker to the rope.

It's a sign cave divers use, so that everyone knows: here is a turn-off.

The direction a marker points to can also be felt,

which means that you can find your way back even in total darkness. They say.

Little by little, we pull our guide rope behind us through the cave

and continually fasten it to specific sections -

as according to the Greek legend, Perseus once did,

using a ball of wool to find his way in the Minotaur's labyrinth.

We need a similar form of reliable guidance, as without it,

even the pros can lose their way down here. I knew I should have taken up knitting.

We're now diving through our first hall. During the course of millions of years,

a forest of stalactites and stalagmites has formed here.

In the light of our diving lamps,

the petrified water droplets have a ghostly appearance.

Then, out of the blue, our first find!

Florian has noticed a dark irregularity on the floor of the cave.

This must be the prehistoric fireplace we were told of.

A C14 analysis revealed

that a fire had burned here 8400 years ago.

The caves were not completely flooded at that time

and were inhabited by both humans and animals.

The fireplace has been perfectly preserved

due to the slowly rising sea levels. An intriguing notion,

to think that here, where we are diving, Stone Age people once lived:

And that this piece of charcoal is a relic from a time,

many thousands of years in our past.

We dive further. Our path continuously leads us through new stalactite formations

They hang from the ceilings of the caves like spearheads.

Inspiring fear, yet also fascination - in that order.

Then we make our next find! We discover a ceramic vessel on a small hill.

The shape and the workmanship suggest that it is from the Maya period.

The sediment and woodchips surrounding the find site

lead us to believe that it probably fell through a long-since buried cenote.

Christian films the vessel from all sides

to be able to examine it later.

Immediately next to it, Florian measures another vessel.

He records the data in his wet notes, a special notice block

made of water-resistant paper.

The vessels could have fallen down here whilst collecting water.

This could be in individual cases, but therefor they are found to often.

It is assumed that they are Mayan offerings. Incense, flowers

and even food were offered to the gods in receptacles like these.

But rites also took place in which the cut out hearts

of those sacrificed were offered

to the gods of Xibalba in clay pots.

Just which version and with which frequency this happened,

is almost impossible to ascertain.

What we find on a nearby ledge is not the first small,

dead Maya of our expedition, but unfortunately, just the skull of a monkey.

But time is of the essence. The discovery bug or not - we have to go back.

The oxygen reserves in our bottles limit our stay down here.

We are aware of the fact that we are simply guests

in this fascinating underwater world.

It is easy to lose track of time in this spellbinding and alien environment,

which makes the confrontation with the inevitable harsher still.

It's not advisable to surface when in narrow places and with miscalculated

time limits. I can almost make out the lid of my coffin in front of me.

Taking no risks,

we begin our return journey with Christian in the lead.

Our guideline leads us safely back, out of the labyrinth.

Back into daylight. Back from Xibalba, the underworld, the place of no return.

Tree roots that have grown through the limestone and now hang in the water

assure us that we are nearing the surface. We have almost made it

and just have to fight our way through a thicket of aquatic flora.

Of course, this was a completely different cave to those we have dived in before.

It's a mixture of both light and dark. The stones are bright enough,

but there's a lot of silt, detritus - all dead plant material -

distributed throughout the entire cave.

In all of the rooms.

And there, on a small pedestal there is this broken pot,

that's really great. it looks fantastic.

We're now on our way to (Denote Zapote,

a so-called sinkhole.

This means, there is only one way - down. There are no turn-offs.

The usual procedure - unloading bottles and equipment.

But before anything else, Robert has to ask the gods for permission.

I'm told the backflip is his annual ritual.

We call this cenote Hells Bells and the name didn't come about quite by chance.

In the course of the millennia, huge bell-shaped stalactites have evolved here.

That makes this dive site really special.

They're really big, some of them measure two metres.

Hanging from a single point on the roof,

they look just like bells. They are absolutely impressive.

In fact, we have never seen anything quite like this before.

Without doubt, this is one of the most beautiful dive sites I have ever been to.

And I'm really looking forward to diving back down there again.

So let's get down to Hells Bells.

We're going down. Soon, our lamps will be the only light source

in the unreal darkness of the cenote.

At approximately 30 metres, we encounter a so-called halocline:

a mixed layer of fresh groundwater and salt water, a vertical salinity gradient,

which is flushed into the caves owing to the proximity of the sea.

The fresh, or low salinity water swims above the salt water

due to the differing weight specifications of the two types of water.

The result is a mixed layer in which vision is slightly impaired.

It's not easy to find your way in this.

But underneath this, visibility is back to normal again

and we continue our descent. We dive through a crevice

...and there they are: Hells Bells.

An unreal world reveals itself, albeit partially fuzzy,

embedded in the watery foothills of the halocline.

Hundreds of bells - some two metres in diameter,

others seemingly tiny in comparison.

The very sight of them is truly arresting.

The light from our lamps refracts green. A sure sign,

that the composition of the water down here is different

to that of the upper regions.

The colour of the light refraction and the concentration of airborne particles

suggest a high sulphur content. This is logical, as the bacterial decomposition

of organic material passing down releases sulphur when it decays.

There are several theories regarding the origin of these bell-shaped oddities.

The most popular of these assumes that due to specific bacteria

on the surface of the subterranean lake, lime was precipitated.

The sinking water level caused these rather special stalactites

to increase in size, larger and larger. There was no water in the cave at this time,

enabling the bells to develop as a special form of stalactite.

This phenomenon is also referred to as a “showerhead”,

being as it is reminiscent of a domestic showerhead distributing water.

And all of a sudden, faced with this unreal world, it no longer seems so absurd,

that this place should be the entrance to the underworld.

In Xibalba, after his death, a man had to go through many tests and trials

before he could enter paradise.

Just as we have to endure the rigors of cave diving

to be able to explore this fascinating, mysterious world. I must admit,

it's quite scary - on the one hand, swimming around at the very gates

of hell itself, and on the other, the very real dangers down here in the deep.

And now it really is time for us to begin with the return journey.

At depths of 40 metres, the pressure on our bodies is immense.

This has to be regularly monitored during our recent,

to reduce the risk

of any of us getting the bends,

the dreaded diver sickness.

Whatever happens, as far as we're concerned, Hells Bells is the belltower

of Xibalba, a place that brings the mysticism of the ancient Maya back to life.

We write the year 900 AD. The king seeks advice from the gods,

as a drought plagues his country.

His people still have faith in him, but his supposedly divine power is beginning

to crumble in step with the rise in famine.

Thus, he has war fought against his neigh- bours and the bloody harvest was abundant.

Prisoners are dragged into the jungle.

The King dances with the Gods. He is their descendant. He will appease them.

The chosen must see the honour bestowed upon them.

As sacrifices, they will immediately enter paradise

and will not have to endure the suffering in Xibalba.

But either way, they have no choice in the matter...

And so, the legation of the priest reaches the sacred caves, here,

the power of the gods is exceptionally strong. It is yours, to beg for admittance,

should you not want to incur their wrath upon you.

The king awaits them. It is his duty to appease the gods with blood.

For his people, for his power.

Back to the present. We have permission to dive in Las Calaveras,

the Cave of the dead Maya.

For this dive Florian and his team

have ordered a special gas mixture.

We use a substance known as nitrox, which is oxygen-enriched air.

It allows us to work underwater for longer.

The nitrogen is always the main problem when diving. it can saturate

and at some point in time, it forces us to come back outside again.

When we reduce the nitrogen levels and increase the oxygen,

we can't dive so deep,

but in the cenote we only have 12 metres anyway

and therefore more effectivity underwater.

First of all, we have 13 metres of abseiling to do in the cenote.

By means of a pulley, our Mayan aides have to manoeuvre each piece of equipment

individually and then place it into the water.

Exhausting work, at 38 degrees in the shade and with humidity levels of around 90%.

It's all downhill from here - in the most positive sense. Sunlight shines through

the rock crevice, causing light fingers or rays of light.

Dramaturgically, a fitting start to our descent

into the caves of the dead Maya.

The name Calaveras actually comes from the finds that have been made herec

as Calaveras is Spanish and means skull, or deaths head skull, to be precise.

Two years ago, Mexican researchers discovered 126 skeletons

from the Maya period, on the floor of the cenote. We are not quite sure

whether it is a Maya cemetery, or a cenote, reserved for human sacrifices.

In both cases, it remains a sacred place for the Maya.

Florian is busy measuring a human hipbone.

To touch or take something with you from here is strictly prohibited.

He jots down the data gathered in his wet notes.

Beneath the mantle of darkness, the first skull is pried from the ground.

The filed teeth are proof,

that this is definitely a Mayan skull, roughly 1800 years old and well preserved.

Polished, sharp teeth, sometimes even decorated with jade,

were very popular amongst the contemporary fashion conscious.

A little further to the left is a pile of human bones.

These bones form the basis of a theory

that they were used in human sacrificial ceremonies.

Apart from a few fragments of pottery, there are no offerings to be found in the cenote.

Some of the skulls do reveal injuries.

Research into this however, is a task for the future.

Meanwhile, Uli is taking pictures of the skeletons. In a close cooperation with INAH,

Mexico's official archaeological authority,

the team constructed special 3D MODELS in 2010. The object was to examine

the finds in more detail, independent of diving times and the raptures of the deep.

The area, or field, is divided into grid squares.

Each find is precisely documented and registered.

There are many mysteries waiting to be solved down here

but our journey continues; and with it, our fascination.

What I see is simply the incredible potential here.

I think we're just about scratching the surface.

There's so much here to discover, there are thousands of cenotes.

There are hundreds of kilometres of cave systems. Actually, almost everywhere

you jump in somewhere, in every cenote,

there are always artefacts from the Maya period.

And deep in the caves is where you can make so many prehistoric finds

animal and human skeletons.

Actually, down here, it's a paradise for underwater archaeologists.

The largest cenotes in Yucatan are lake-like incursions in the barren limestone.

Their dimensions can easily be those of a lagoon.

But why did the Maja transfigure the watering places?

Well, if one recalls that, apart from the sea in Yucatan,

there are no rivers flowing anywhere on the surface,

it seems quite logical.

Access to water is only possible via caves and cenotes.

This is why the Maya declared water to be divinely transfigured.

An approach, similar to many indigenous peoples in Africa.

Guards watch over the water here too.

He who has direct access, after all, has divine power.

Many cenotes in the Yucatan are fed by the Ox Bel Ha cave system.

In the language of the Maya, Ox Bel Ha means “three paths of water”.

This system transports fresh water inland below the jungle,

through the mangrove forests on the coast, to the sea.

The Mayas knew the ways of the water exactly and for this reason,

were able to found their culture on subterranean water.

That's why the largest Mayan temples are to be found in the proximity of cenotes.

These secured the welfare of those who settled close by.

Back to our expedition. The briefing prior to our next dive.

We dive here right after the entrance on the left line at the first T,

then down the corridor, keeping left - that's the route

we already know. We take the jump to the right,

we saw how that worked last time. This is the big arrow

and then we dive into the saltwater. it's around 15

to 20 metres deep and we run into the halocline, the layer between

fresh and saltwater. Then we reach this huge tunnel,

there. Here, this big tunnel,

with the main rope.

It means we have to get stuck in again,

and lay a jump on the guideline here.

And when we're here, we'll start prospecting this area here

and then this one here. And one of us remains by the guideline

so that he can see at at all times... and the others,

one takes care of the left, the other the right.

Then we'll see whether we can find

the assumed prehistotic bones.

Something very prehistoric is suspected within this cave system.

Florian can hardly wait to get started and in fact,

our combined curiosity has been sparked.

The first surprise awaits us shortly after jumping into the water.

A cave of breathtaking beauty reveals itself,

as if it were a gigantic underground train tunnel.

But one should never forget the safety pre- cautions. Robert demonstrates what can

happen when you thoughtlessly flap your fins. Down here, the sediment

practicly just rests lightly on the seabed. One wrong move

and visibility is zero.

We dive through a fissure. Not the very best for those of a claustrophobic disposition.

The crack is just wide enough for us to swim through without our bottles getting caught.

Our breath accumulates directly beneath the ceiling and looks like liquid mercury,

hovering immediately above our heads. Like a scene from a science Fiction movie

set in which the silver surfaces constitute the transition into another world.

I look around, I must admit that it looks as though we've

already arrived in this “other world”.

Should the safety rope ever tear, the silvery bubbles beneath

the ceiling serve as a signpost toward the exit.

We've heard quite a few stories whereby cave divers

who had lost their safety's still managed to save their own skin

by using this trick and following the bubbles right back to the exit.

We penetrate even deeper into the cave. Past stalagmites

that look like piles of sand.

Fragile details and bizarre shapes directly adjacent to them

give the impression of a recent landslide - only one forged in stone.

Uli christened this stalactite “The sword of the Underworld”.

I must admit, seen in the light of his lamp, the scene has something oppressive about it.

We continue our dive. Yet another cave ahead of us.

A forest of columns is an impressive image. Fragile and staggered in depth,

one column next to the other: Each of them different, each of them unique.

By the way, more than anything else, it is the stalactites and stalagmites

that are proof that these caves were not always underwater.

The limestone does originate from a time

when Yucatan was beneath sea level, but during the last ice age,

the sea level was around 100 metres lower than it is today.

Causing the massive limestone plateau to dry out.

Rain penetrated into the porous stone, dissolving minerals, and as it dripped from

the ceiling, stalactites were formed: and those that began to grow toward them

from the ground over the millennia are known as stalagmites. It wasn't until the sea level

gradually began to rise again, at the end of the last ice age,

little by little, the caves were once again flooded.

We've been on the move for quite some time now. I wonder

where this tunnel leads? I feel a bit panicky, actually.

We've come quite a way within a branched cave system

and there is no other exit other than the way back.

What are we going to do? Keep calm and all that. I know, don't waste air.

I manage to calm myself down.

Suddenly, the cave opens and we appear in the middle of the jungle

in a different cenote.

Thanks, Uli. You knew that it would work.

Fantastic, absolutely fantastic.

Not bad.

Just how huge is this tunnel actually?

Huge corridors, fantastic formations. The colours of the cave, the thermocline,

the halocline. So indescribable.

The tunnel is similar to a train tunnel. You just look to the left and to the right

and wait until the metro drives by.

And the entrance is relatively tricky too. You have to dive here first.

You won't be able to see anything again as it's full of sediment and crap.

You can feel your way forward bit by bit using the lead lead and at some point

you'll fall in this cave here and everything will be crystal clear again.

And then you have this cave system to deal with.

Very funky, the whole thing.

After a short break, it's time to move on.

We haven't found anything vaguely prehistoric as yet,

but we have another junction, another fork to explore.

Perhaps we'll find something there. We change the tanks

and make ourselves ready for a further dive.

We're not about to give up quite yet.

And once again, it's back down to the flooded underworld

in search of relics of the past.

Slowly but surely, we're getting used to the bizarre formations and stalactites

down here, almost ignoring them as we swim by as if they were nothing special.

We are more interested in prehistoric skeletons, remains of animals from

the Stone Age. My patience is dwindling.

We leave some of our bottles behind

behind and fasten them to the guideline. The side tunnel is narrow

and the additional tank at our side - the so-called Stage -

is only intended for the return trip anyway.

We discover the side tunnel

and now regulate our further procedure with previously defined gestures.

Sign language is the only language that works properly down here.

We're laying a jump from the guiderope,

a fork into the still unknown side tunnel. Then we continue to dive,

always with the rope in our sights,

which of course is absolutely vital, especially here in uncertain terrain.

Our movements cause ancient sediment to crumble from the ceiling,

which is a sure sign that this area has seen little exploration up to now.

Then, at long last, Florian discovers the skeleton from which we had heard.

Well, that's the way to get the pulse rising.

Uli takes some shots to keep everything nice and neatly documented.

It seems to be a megatherium, a kind of prehistoric giant sloth.

Around 10.000 years old and well-preserved.

Giant sloths could be anything up to five metres in length

and weighing several tons. This animal appears to have lived here,

as in the caves it could not only find refuge but also water.

The skeleton looks eerie in the flickering light of the halocline ahead of us.

We dive on to the next cave.

Who knows, we may find something else on a day like today.

Looking up, I can't help but be fascinated by the sight of our own spent breath,

which is gathering above me on the ceiling. For a moment, it looks as

though the air is gushing out of the rock. But in fact, the opposite is the case.

After a few hours, the air will have found its way to the top through the rock.

The rock structures in this cave have something primordial

about them. This is reminiscent of the nave of a church.

Gigantic stalagmites rise up from the middle of the room.

Wait, there is something there, behind the rock.

At first, it can hardly be distinguished from its surroundings,

until Robert notices the white spots.

With his lamp, he indicates for us to come closer.

Then, the closer he gets, the clearer it becomes.

The lower jaw of a huge animal

of apparently prehistoric origin. Right in front of us.

It once belonged to a mastodon, an elephant-like animal

that lived here many thousands of years ago.

Biologist Robert is clearly over the moon.

A spontaneous lecture in sign language follows.

These teeth were perfect with which to crush branches and leaves.

Strictly speaking, these here are two parts of the lower jaw, very well preserved.

Mastodons were smaller, yet stockier than their relatives, the mammoths.

We can hardly believe our luck - two huge finds from the Stone Age in one day!

But now, we really have to get back. The air supply is slowly running out.

The jump will take us safely back to the guideline.

Then we take up our stages again. The additional tanks we left behind earlier

on will supply us with enough air for surfacing.

Here, Flo demonstrates how he changes from his back gear

to the stage at his side.

Everyones ready to go. So, let's do it.

We dive through the halocline at a different location, experiencing

yet another especially bizarre moment:

dead branches, as if they were gnarled fingers,

show us the way up to another exit.

Robert is still excited as he relives the last dive.

We found part of a mastodon mandible.

There were actually two completely preserved teeth in the lowerjaw.

One tooth was really 20 centimetres long,

weighing at least one and a half kilograms, but it was unfortunately broken.

The second tooth was 15 centimetres longer.

Just ONE tooth, that is brilliant. As we made this discovery,

it was very special,

it was really very special. And you could see grooves

on the back molars,

which means that this animal was somewhat older.

Really, the teeth were totally ground away. This happens to us as well.

We are constantly grating and grinding out teeth away!

But I'm sure that the rest of the mastodon

is somewhere inside there. It's a very muddy Cenote

Cenote and we just about managed to discover this mastodon jaw.

But I'm sure that the rest is down there somewhere.

We just have to go back in and look for it.

The next day. We prepare for the last

and most extreme part of our expedition.

We learned the cenotes are connected to the sea.

But can you dive through the caves and into the sea? We want to find out.

According to the map, there are several kilometres to overcome,

which is virtually impossible without scooters.

But before we do anything else, we have to get some Trimix, a special gas mixture for

deep Sea diving. For safety reasons, every bottle is carefully examined.

Trimix consists of helium, oxygen and nitrogen.

We now analyse the gas, that is, we check

how much bar we have in the bottle and

exactly what gas mixture is inside.

This is quite simply important

important because gases in certain depths react toxically.

We would have a problem if we have too much oxygen in the bottle and find

ourselves at a certain depth. This could turn into a potentially dangerous situation.

This is why everything is exactly analysed,

then labelled with date and name,

so that everyone knows which gas he has

to whom it was assigned and we can therefore

exclude mistakes when diving. it's very important to do this in advance.

Should there ever be an accident, errors can be traced

more efficiently this way. Whether this is during analysis,

or whether something went wrong during the further course of a dive,

or it's just documented, which gas mixture

is being breathed in the depths.

The checks have all gone well. Now we just have to load the new bottles onto the pickup

and we can get going.

Our start cenote is situated in the middle of the jungle. We have determined our exact

position by GPS and estimate

that we should be able to find a way into the sea from here.

First of all we have some equipment humping to do, all the way to our mission base.

We're glad everything's ready and ship-shape and can jump into the water at last.

We have several hours of being underwater ahead of us.

On to the final adventure, our dive from the heart of the jungle into the sea!

To cope with such a long distance, we need underwater scooters,

torpedo-shaped mobility units,

with which we can almost treble our speed.

And let's not forget, how much fun these things are.

We glide through the water like fish.

Formations pass us by as if in time-lapse.

We dive through one cave to the next with ease, ever deeper into the system.

These Scooters are like a Formula One ride through the underworld.

We shoot through the Kingdom of Xibalba en route to the coast,

much faster than without the technology.

And otherwise, the gas reserves in our bottles would never be enough.

We find an initial breakthrough. Hanging mangrove roots

as they occur in coastal areas show us that we are on the right track.

Algae stretch toward us as we pass through the gap.

Have we already reached our destination?

We surface and find ourselves in the mangroves of the riparian strip.

At the moment, we are only separated from the sea by a very thin barrier. So, we head

down again and look for another passageway.

It takes a while, but then we find another gap,

through which we can see light from the other side.

We dive in.

Our first contact with the sea is blurred. Right in the middle of the tunnel

as if it were a wall, is a halocline. For one brief moment, we have zero visibility

but don't lose our orientation.

Then we're through. Pure adrenaline.

It worked. That was fabulous, a great dive.

Toward the end through the mangrove woods,

then through the beach section. It got dark then again

and here, up front is a tiny gap. You can see light through it,

although it was relatively milky due to the halocline.

And then, all of a sudden, plop - and then you're through, you've made it.

Our last dive has closed the gap between the enigmatic

Maya world and the sea.

The Yucatan cave system empties itself into the sea by means of a continuous current.

We could experience this first-hand. The basis for fresh drinking water.

The Maya recognised this and built their religious sites

in the vicinity of the cenotes.

This was in fact the key to the emergence of their civilisation.

One thesis for their demise is a prolonged drought,

which destroyed their social structures.

The climate catastrophe could not be averted, even by increasing

human sacrifices. Wars and secession shook the very foundations of the kingdom,

causing the power structues of the Maya to collapse.

We have explored the once sacred places of this advanced civilisation.

We've experienced the adventure of cave diving and overcome

the biggest challenge a diver can face.

In doing so, we were able to admire the amazing beauty

and uniqueness of the cenotes.

Xibalba put us through our paces, and gave us a hard time.

But in the end, we DID return from the realm of shadows,

the depths of the underworld and the caves of the dead.