The underground lake of Saint-Léonard is the largest underground lake in Europe, 300 m long and 29 m wide. It lies between the towns of Sion and Sierre, in Switzerland, in the Valais Alps. It was discovered in 1943 and operated since 1949. It is navigable and its water is constantly at 11° C. As the cave is completely submerged, all tours are done aboard rowing boats with around 40 people at a time. Inside the cave, there is the statue of Saint Barbara, patron saint of geologists. You can also enjoy the beauty of the vineyards which lie just outside, above the lake.
To make the visit, you must register online. It is possible from March, 19th to November 1st. The visit lasts half an hour in the company of a multilingual guide.
Children under 5 enter for free.
If you usually feel the cold, bring a sweater or jacket because the temperature there is around 15 degrees.