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About this place
The Saint-Léonard Underground Lake (French: Lac souterrain de Saint-Léonard) lies inside a hillside in the municipality of Saint-Léonard, in the Swiss canton of Valais, roughly halfway between Sion and Sierre. It is regarded as Europe's largest natural underground lake that visitors can tour by boat.
What is it?
The cave sits beneath vineyard slopes, tens of metres below the surface. The lake measures about 300 m long, 20 m wide and up to 10 m deep. The air stays around 15°C all year, so it feels cool in summer and mild in winter.
Europe's largest artificial underground lake is the Seegrotte in Hinterbrühl, Austria, built by people. Saint-Léonard, by contrast, is entirely natural.
What does the visit involve?
The whole tour happens on the water. Visitors board large rowing boats that carry up to 40 people. The trip lasts around half an hour, with a guide explaining the cave's story in French, German and English. Lit sections show the rock ceiling and walls reflected in the still surface.
What is its history?
Official accounts say the cave was first entered in 1943, when the water level dropped in spring. Jean-Jacques Pittard is named as its explorer. The lake opened to the public in 1949 and has been a regional attraction ever since.
How do you get there?
The entrance is at the foot of the hill in Saint-Léonard, at about 46.26°N, 7.43°E. Sion and Sierre lie on either side of the village, so the drive from either is short.
When should you go?
The attraction is seasonal, running from March to November. Check lac-souterrain.com for current hours and prices before you travel, as they vary through the season. Because the temperature underground is constant, it works well on a rainy day. Bring a light jacket on hot days.
What else is nearby?
The Sierre and Sion area is the heart of Valais wine country. After the cave you can stroll among the vineyards on the Rhone valley slopes or drive on to Sion or Sierre.
Frequently asked questions
Is it the largest underground lake in Europe? It is the largest natural underground lake in Europe open to visitors by boat. The artificial Seegrotte in Austria covers a larger area.
How long does the tour take? The guided boat ride lasts about 30 minutes. Allow an hour including the walk in.
Which languages do the guides speak? French, German and English.
Can you visit in winter? The cave is open seasonally, from March to November. It is closed to visitors in the remaining months.
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