The Saint-Léonard Underground Lake, located in Valais between Sion and Sierre, is billed as the largest navigable natural underground lake in Europe. You explore it by boat on a guided tour that explains its geological origins.
Lakes & ponds
Main highlights
- A navigable underground lake 300 m long, billed as the largest in Europe
- A 30-minute guided boat tour with commentary in French, German and English
- Large rainbow trout swimming in the lake’s isolated waters
Overview
This underground lake lies hidden beneath the vineyards of Saint-Léonard, between 30 and 70 m below ground. Discovered in 1943, it bears witness to the formation of the Alps. The limestone cave that holds it was shaped by thousands of years of erosion.
The lake is 300 m long, 20 m wide and about 10 m deep. The cave stays at a constant 15 °C all year round, so it feels cool in summer and mild in winter.
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What to see and do
Visits are guided only, aboard traditional boats that glide across the lake’s crystal-clear waters. The guide explains the cave’s geological origins in French, German and English. The trip lasts 30 minutes and lets you admire the rock walls, highlighted by colourful lighting.
On weekdays, excluding weekends and public holidays, a dynamic tour is offered : the lighting changes as the boat moves along, revealing the cavern’s various nooks.
In the water, you can spot large rainbow trout living in this environment cut off from the outside world. Thanks to its acoustics, the cave also hosts concerts, which the audience enjoys from the boats.
Practical information
Getting there : the lake is in the village of Saint-Léonard. Saint-Léonard station, on the Sion-Sierre line, serves the site.
Visit length : the boat trip lasts 30 minutes, with departures at set times.
Suitable for : the tour is family-friendly and accessible to people with reduced mobility with assistance.
On site : free parking and boarding from a secure platform.
Visiting tips
Booking is required for all tours. Book ahead, especially in summer, and arrive 15 minutes before your scheduled time to check in.
Bring a warm jacket : the cave’s 15 °C feels chilly after the heat outside.
Nearby attractions
- Happyland is a nearby amusement park designed for young children.
- The Longeborgne Hermitage, nestled in a cliff in the Borgne gorge, is a Valais pilgrimage site.
- Tourbillon Castle, former residence of the bishops of Sion, offers panoramic views over the town.
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