Lac Souterrain St-Léonard

The Underground Lake of Saint Léonard

Useful Information

Location: 6 km east north east of Sion on the Sion-Sierre road.
Open: 15-MAR to MAI daily 9-17. JUN to SEP daily 9-17:30. OCT to 01-NOV daily 9-17. [2006]
Fee: Adult CHF 10, Children (5-16) CHF 5. Groups (12+): Adults CHF 9. Plus tip for the boatman. [2006]
Classification: Speleologygypsum cave
Light: LightIncandescent Electric Light System
Dimension: L=300 m (cave), L=260 m (lake), W=15 m, A=509 m asl., T=15 °C (air), 11 °C (water), V=100,000/a.
Guided tours: D=40 min, completely by boat. (English Deutsch - German Italiano - Italian Français - French)
Bibliography: André-H Grobert (1987): The subterranean lake of Saint-Léonard (Valais-Swiss), 12 pp, 2 colour photos, survey, SB.
Address: Lac Souterrain, Jean-Marc Bürgi, Case postale 75, 1958 St-Léonard, Tel: +41-27-2032266, Fax: +41-27-2032266. E-mail: contact
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.


APR-1943 first explored by members of the Société Suisse de Spéléologie.
1946 an earthquake creates fractures in the rock which results in loss of water.
1949 developed and opened to the public.
1950 the cave is consecrated to the Notre-Dame des Gouffres by a local priest. A sculpture is placed on the shore of the lake.
2000 cave closed for renovation.
16-JUN-2003 reopening.


At St. Léonard, on the main road between Sion and Sierre, on the right bank of the Rhône, 5 km from the capital of the Canton of Valais, is the largest underground lake in Europe. The cave is formed in gypsum, about 260 m in length and 15 m wide. The cave was discovered in 1943 and commercialised in 1949. Here, close to the entrance of the lake, visitors can enjoy a moment of agreeable relaxation with a large car park and a refreshment room set in a pleasant, quiet and cool garden. A boat trip on the wonderful clear water of the lake gives one an opportunity to admire the rich, harmonious and varied subterranean geology.

Text by Tony Oldham (JUN-2001). With kind permission.

The cavern with its lake was known for a very long time, at least the entrance and the shore of the lake. But the locals did not enter the cave, and foreigners did not visit this secluded spot. So the first exploration, with the discovery of the huge lake, happend in 1943.

In the centuries before the cave was explored, several legends about the cave developed. One tells about a young man who was trapping around the cave entrance. He discovered leaves of stone in the cave entrance and picked one up. To his surprise a heavy wind arose out of the cave, across the lake. When the wind calmed down again, the leaf had become two golden coins. But whenever other people tried to do the same, it never happened again.

Another legend tells that young maids, visiting the lake at midnight of December, 24st, will see the reflection of their future husband in the dark waters of the lake.

The cave is located in a layer of anhydrite (gypsum) which can be found along the Rhone valley around St-Léonard. It reaches the surface for three kilometers, between St-Léonard and Granges. It was quarried sometimes, but this is not profitable, as the gypsum is very impure.

The anhydrite was originaly deposited in an aride climate during the Eocene (58-37 Ma ago) in a cove of the Tethys sea. During the formation of the Alps, the layers of sediments were moved and displaced in so called nappes. The anhydrite of St-Léonard belongs to the Pennine nappe. After its dislocation it is now tilted by 90° and stands upright, enclosed by schist to the north and slightly metamorphic limestone to the south. The cavern has a ceiling and floor of anhydrite and parallel walls of schist to the north and marble to the south.

The cave itself is very young, as caves in anhydrite form very fast. It was dissolved by meteoric water which solutes great amounts of anhydrite. At the moment there is no real exchange of water. Connections to the surface seem to be sealed by clay, and only a little amount of water leaves the cave towards the entrance. To keep the water at the same level some water is pumped into the cave.

The cave was closed for renovation but is now reopened. The new administration is very enthusiastic and will do its best to make each visit unforgettable.