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The Lost Sea Lake is the World's second largest underground lake.
© Lost Sea
Exploration
Be amazed by these 10 underground lakes
From a body of water the size of Sydney hidden beneath a glacier to a lake sat right beneath another lake, discover some of the most amazing places you can find under the earth’s surface.
Written by Will Gray
5 min readPublished on
To discover the planet’s most amazing places, you have to go to its extremes – and these underground lakes are on another level.

1. Salina Turda

Constantin Popovici of Romania dives at Salina Turda, Romania on October 7, 2020.
A spectacular setting for a bit of cliff diving© Mihai Stetcu/Red Bull Content Pool
120m under the surface of the Earth, a science-fiction-like wonderland shaped by salt and humankind exists called Salina Turda. It’s one of the oldest salt mines in the world, first used nearly one thousand years ago.
These days Salina Turda is a popular destination for tourists and in 2020 received two very special visitors. In a never-before-attempted feat, Red Bull Cliff Diving stars Rhiannan Iffland and Constantin Popovici pushed the boundaries of their sport to the next level. The duo leapt from the walls of the cone-shaped mining room into the underground salty lake. On impact with the water the athletes’ bodies were decelerated from 85kph to zero in almost twice the usual speed, due to the underground lake’s high density.

2. Owey Island Lake

The underground lake under Owey Island in Ireland.
The lower lake of Owey Island where the walls glow under torchlight© Unique Ascent
This is a lake beneath a lake – with the underground one sitting 50m below the one on the surface.
It sits in a 150m long and 40m high cavern and ends at the 8m wide ‘Pool of Tranquility’, which sits in complete darkness. Access is through a narrow hidden sinkhole leading to a tunnel covered in bioluminescence, which makes the walls glow under torchlight. But fresh debris fell from the roof last year – slightly concerning given the upper lake is directly above!

3. St Leonard Lake

The Swiss lake is Europe’s biggest underground lake.
Saint-Léonard Lake is vast© Borsic at English Wikipedia
At 300m in length and with a surface area of 6,000 square metres, this is Europe’s biggest underground lake.
It’s around 200 years old but only began to be really explored after 1946, when a giant earthquake opened up fissures and lowered the water level, making it more navigable. It has been open for public boat rides since 1949 – but was shut for three years in the early 2000s when the roof began to fall in and had to be fixed by 5,000 ceiling bolts.

4. Cold Cave under Cross Mountain

Inside one of the world’s largest natural cave ecosystems is a chain of more than 45 emerald green subterranean lakes.
Small sinter dams, which are formed wherever the water flows over rapids, separate the lakes, some of which are up to 7m deep. The entrance has high ceilings and a large lake but from then on it becomes more expeditionary and access, in small rubber boats, is limited to just four people a day.

5. Lake Vostok

  • Where: Vostok Station, Antartica
This is the largest of Antarctica’s subglacial lakes – and at 250km long and 50km wide it’s around the size of Canada’s Lake Ontario.
Buried by ice for more than 15 million years, it sits 3.8km beneath the surface at the Pole of Cold and is believed to be home to a unique ecosystem based on chemicals in rocks instead of sunlight. There’s no way of going there though – it took two decades to drill a borehole to allow small scientific probes to reach its surface.

6. The Lost Sea

The largest underground lake in the USA lies deep inside Craighead Caverns, which were once used as a Cherokee hideout.
Sitting 42m under the surface, the lake is 240m-long, covers an area of over 16,000 square metres and contains several cave ‘rooms’ completely filled with water. Its shoreline is filled with rare anthodites, better known as ‘Cave Flowers’, and it can easily be accessed via a hike and a boat tour.

7. Reed Flute Cave

Reed Flute Lake in all its glory
Reed Flute's motionless lake is lit up by the colourful limestone cave© Dennis Jarvis from Halifax, Canada
This stunning lake acts as a mirror for the natural limestone sculptures inside China’s ‘Huge Art Palace of Nature’.
The 240m cave was once used as an air raid shelter but has been converted for tourists and the cave now reflects stalactites, stalagmites and stone pillars shaped like birds, plants and animals, all painted with colorful lights. The walls contain ink inscriptions dating back to the Tang Dynasty in 792AD.

8. Hang Sơn Đoòng

The British caving team inside the Hang Son Doong cave in Ke Bang Massif, Vietnam, in 2009.
Hang Son Doong was discovered by a British caving team© Barcroft Media/Getty Images
Revealed to the world less than 10 years ago, this is the largest cave on the planet - and contains not just a lake but an entire river system.
The fast-flowing water inside carved out the 9km long cave, which is more than 200m wide and 150m high, but the location is so remote and so tough to reach it takes a week to explore. Rising water levels cut it off for half the year and fewer people have been inside than have summated Everest.

9. Sistema Sac Actun

  • Where: Yucatan, Mexico
Sistema Sac Actun - Diving cenotes in Mexico
Into the light... © Luis Leal
OK, this is more of a flooded cave system than an underground lake, but with 345km of submerged watery tunnels it deserves a mention.
Winding underneath the famously porous Yucatan region, these networks of tunnels can be accessed by the many Cenote sinkholes on the surface including Grand Cenote, just outside Tulum. The entire system, which is the world’s biggest underwater cave, was only finally mapped out this year.

10. Grjótagjá

The lake can be found in a small lava cave
Geothermal waters© Hansueli Krapf
This naturally heated lake sits under a dramatic fissure and although recent activity has made it too hot to take a dip, it’s still a stunning place to visit.
The only sign of its existence is a dramatic tear in the earth’s surface above it, but a tricky climb down leads to a sparkling serene escape from Iceland’s winter chill. Its use in Game of Thrones has made it a popular tourist spot, but get here at the right time and you can have it all to yourself.
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