St. Leonard Lake – the largest underground lake in Europe


The largest navigable underground lake in Europe, St. Leonard Lake or Lac de Saint-Léonard, is located between Sion and Sierre. This fascinating water grotto is easily accessible and can be explored on a boat tour. The boat guides provide interesting information about the geology and history of the cave.

Lake St. Leonard in Valais is known for its crystal-clear water and impressive underground caves.

Underground St. Léonard Lake

At a height of ten meters, the different types of rock shine, their shapes reflected on the 6,000 square meter surface of the lake. Trout swim around in the clear water, while the only truly indigenous creature in this subterranean world, the fungus gnat, attaches its larvae upside down to the cave walls.

The underground lake of St. Leonard is an experience in itself. The underground lake stretches over 300 meters in length and around 20 meters in width and has been used for tourism since 1949. Every year, around 80,000 visitors are taken across the lake in large boats. According to reports, the renowned speleologist Jean-Jacques Pittard was the first person to explore the cave.

The lake is a popular excursion destination, inviting visitors to go on boat tours and explore the fascinating underwater world and the geological formations of the caves.

More information on visiting times at: Lac Souterrain de St. Leonard

Video Europe’s biggest underground lake

The largest underground lake in Europe is in the southern Swiss canton of Valais in St-Léonard…

Europe's biggest underground lake

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