Easy to miss from above, some of the world’s most spectacular lakes are hidden underground. From a lake sitting beneath another lake to a body of water the size of Lake Ontario, the world’s underground lakes are just as fascinating and varied as those above ground. Cut off from the outside world, underground lakes have also developed their own diverse ecosystems over time, making them a paradise for nature lovers and scientists alike.
Underground lakes normally form where the rock has been eroded, leaving a cave where water can flow and accumulate. Lakes can also form under glaciers, and occasionally, human activity, such as mining, has led to the creation of underground lakes. Today, many underground lakes are accessible for visitors to explore, and their undeniable and unique beauty has made them popular tourist attractions in their own right. Where are the world’s 10 best underground lakes?
10 Reed Flute Cave, China
Located near the city of Guilin, Reed Flute Cave is made of natural limestone. Inside, the cave is illuminated, allowing visitors to admire the underground lake in all its glory. The walls of the 787-foot-long cave feature cave paintings that are believed to date back to the Tang Dynasty in 792 AD, and its name derives from the reeds which grow outside the mouth of the cave, which are used locally to make flutes.
9 Kow Ata Underground Lake, Turkmenistan
Situated deep below the surface of the earth (200 feet, to be exact) in Bäkharden Cave, this impressive lake is 235 feet long. The water is rich in minerals and salts, and the high sulfur content gives the lake its distinctive smell. Today, the lake’s bath-like temperatures make it a popular local bathing spot, but visitors are not alone – the cave is also home to one of the largest colonies of bats in Central Asia.
8 Krizna Cave, Slovenia
Slovenia is famous among travelers for its stunning bodies of water above ground, such as Lake Bled. However, the country also boasts the magnificent Krizna Cave, which contains a staggering 22 individual underground lakes. Thanks to varying mineral contents, each lake is a distinctive shade of green, and visitors can admire them on a boat trip.
7 Son Doong Cave, Vietnam
Vietnam's dramatic scenery is world-renowned, and the country is also home to the largest cave in the world (9 km long by 200 m high at its highest point), containing a lake near its mouth. The lake’s water level is dependent on the adjoining river, and during the rainy season, it becomes inaccessible due to the dangerously high water levels. At other times of the year, a permit is needed to access the cave and its lake. As such, very few people ever entered the deepest parts of the cave.
6 California Cavern, USA
The California Cavern is a sight to behold at any time of year, but especially in winter when the heavy rains bring it to life and fill the cave’s underground lake. Its crystal-clear waters delight visitors who come for a swim, and there may be more to enjoy in the future, too, as explorers continue to uncover untouched areas of California’s longest cave system.
5 Saint Léonard Lake, Switzerland
Switzerland and Austria often battle it out as to which country boasts the better Alps. But when it comes to underground wonders, there is no contest. Saint Léonard Lake is the largest underground lake in Europe, at over 64,000 square feet. The lake used to be inaccessible, but a 1946 earthquake measuring 5.6 on the Richter scale created large cracks in the cave, opening up the lake. In the early 2000s, the roof began to collapse, and so the authorities were forced to close the cave for three years while 5,000 ceiling bolts were installed. Today visitors can float across the lake in safety on one of the many organized boat trips.
4 Owey Island Lake, Ireland
One of Ireland’s most unusual natural features, Owey Island Lake, is a lake beneath a lake! Situated 164 feet underground, the lake is fed by the body of water above and can be accessed via a series of narrow, muddy passageways. County Donegal, where Owey Island is located, is one of Ireland's best-kept secrets, but those who make it are rewarded with the Pool of Tranquility at one end of the lake. This area of the cave sits in complete darkness, but under torchlight, bioluminescence glows brightly.
3 Lost Sea Lake, USA
Tennessee’s Lost Sea Lake is the largest underground lake in the US and the second largest in the world, coming in at a staggering 172,000 square feet. Part of an extensive underground system known as Craighead Caverns, the lake is a hit with visitors who come on boat trips or by foot to admire the surrounding stalactites and stalagmites of one of the most magical caves in the US. It’s full of life, too – the lake contains plenty of rainbow trout and is adorned by cave flowers.
2 Lake Vostok, Antarctica
Lake Vostok is by far the largest of the world’s underground lakes. Situated two miles beneath a glacier, the lake measures an incredible 143 miles by 31 miles, making it larger than Lake Ontario. Its location in Antarctica means that it is nearly impossible to reach for most tourists, but its sheer scale is a sight to behold. Scientists estimate that the lake has been buried underneath the glacier for more than 15 million years, and due to the lack of sunlight underground, it contains little life.
1 Salina Turda, Romania
Deep in the heart of Romania’s Transylvania region lies a unique underground formation. This other-worldly lake is found in one of the world’s oldest salt mines, dating back almost one thousand years. Today, the mine and its lake have become popular tourist spots, attracting visitors who wish to enjoy the health benefits of its extremely high salt content.