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Europe’s Largest Underground Lake Under A Cave In St-Leonard

Last Updated on October 29, 2023 by Admin

Europe’s largest underground lake is located in Saint-Léonard, a municipality in Sierre, Valais, Switzerland. This underground lake (Lac Souterrain de St-Léonard in French) is associated with a cave that you can access via a 30-minute boat ride.

The largest underground lake is located beneath the vineyards of Saint-Léonard. Located on the left side of the Lienne and the right side of the Rhone, theSaint-Léonard area is mainly used for agriculture. The underground lake of Saint-Léonard is an excellent tourist attraction in the canton of Valais.

It is a good day trip from both Sion and Sierre, which are ten to twelve minutes away by car respectively. It is remarkably illuminated in yellow and blue lights, very easy to reach by public transport and boat rides can be booked in advance online.

Saint-Léonard Lake Summary

Total Length:260 meters (850 feet)
Total Width:29 meters (95 feet)
Average Depth:4 meters (13 feet)
Maximum Depth:13 meters (43 feet)
Surface Area:6000 m2
Type:Underground Lake

How was the Underground Lake discovered?

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Discovery of the Lake

Although the locals are said to have known of the cave and lake’s existence many years prior, it has never been explored until 1943.

In 1943, a courageous (or adamantly curious) man named Jean-Jacques Pittard together with his companion Jean Della Santa, took a boat inside the cave. Together, they rode the boat towards the end of the cave where there is a little beach. After having seen enough, they made their way back.

Their efforts helped pave the way for the underground lake and cave to be opened for tourism. It was in 1949 when the lake was finally made accessible to the public. The tourist attraction has since been improved and made safer for visitors.

Renovation Work and Reopening

Though the cave has been open for some time, an accident took place in the winter of 2000. A two-ton heavy rock fell from the ceiling into the lake. As a result, the cave was closed by the authorities for repairs and to ensure its safety.

As a result, the cave was closed for around 2.5 years while extensive renovation work was carried out. The cave ceiling was secured by inserting several thousand large and small rock anchors after several years and 2.5 million CHF.

Having reopened in 2003, the lake has welcomed tourists ever since.

Nowadays, visiting the cave consists not only of the boat ride. You can also read the various information boards in the waiting area before or after your boat ride.

How Do You Get To Saint-Léonard Lake?

The underground lake of Saint-Léonard is located along the main valley of Canton Valais – the Rhone. As it is located under the vineyards, it cannot be seen on normal satellite maps. But do not fear, as it truly does exist underground.

Traveling by Public Transportation

To get to Saint-Léonard Lake with public transportation, you can either do one of the following:

  • Option 1: Take the bus from either Sierre or Sion train station heading to St-Léonard, Le Lac stop
  • Option 2: Take the train to Gare de Saint-Léonard, walk northeast on Avenue de la Gare toward Route du Simplon/Route 9, turn right onto Route du Simplon/Route 9, then turn left onto Rue du Lac. Walking time from Gare de Saint-Léonard train station is 14 minutes.

Traveling by Car

For those with a car, the exact address is:

Case postale 75
Rue du Lac 21
1958 Saint-Léonard

There is a parking lot a few meters away from the underground lake.

What are the Opening Times?

Saint-Léonard is open from mid-March to the beginning of November from 10:00 AM to 5:00 PM. In summer, it is open longer from 9:00 AM to 5:30 PM.

How Much Does It Cost To Visit Saint-Léonard?

The tickets cost CHF 12 per adult and CHF 7 per child (5 to 15 years old). Children under 5 are free.

The boat guides can speak English, French, German, and Italian. They also welcome tips.

What was Our Experience?

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Tickets and Entry

We booked our tickets in advance online directly from the website It was easy and straightforward. As we were assigned a specific time frame, we went around 15 minutes earlier to ensure that we wouldn’t be late and miss our spot.

There was no queue when we came but there were already around 30 people waiting inside as we arrived. Apparently, the system had booked too many people at the same time frame. And so there weren’t enough spots in the boats for everyone. Two boats were moving at the same time (one moving inside the cave and the other moving back out of the cave).

We had to wait around 10 to 15 minutes more due to this inconvenience with the ticketing system. It meant that those who arrived earlier were able to ride the boat on time. However, those who came a bit later had to wait. The extra boat did come as promised, and it was a longboat that was able to accommodate all of us waiting.

Boat Ride Experience

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Once inside the boats, we were ushered in by the boat guide. From the waiting area to the boat, there are many steps going up and down.

Even though it was the peak of summer, the cave was mildly cool. So bringing a sweater or light jacket will definitely come in handy. The guide separated us into languages (German speakers in front, French speakers at the back, and everyone else in between). I guess this will vary depending on the boat guide.

Our boat guide described the cave in much detail throughout our 30-minute journey. It was really fascinating as I had never been inside any underground lake in a cave before. There were pretty lights in yellows and blues.

The boat guide brought a flashlight to help put a spotlight on specific areas of the cave or lake while explaining things. We were fascinated by its history, the clarity and color of the lake, and the mystical feel of the place.

During the ride, we saw fish that seemed to be brown trout. Also supposedly there are bats inside the cave, but we didn’t see them.

Is it worth it to visit Saint-Léonard Lake?

I believe that the whole experience does not cost much and is an overall wonderful experience. I think the price is also totally fair as they need it to maintain the safety of the place (by adding safety bolts) and pay for the employees working in it.

The place is a bit far from Zurich and I wouldn’t recommend it as a day trip from there due to the long distance of traveling from Zurich. After all, the boat ride is only 30 minutes long and possibly not worth the 3-hour journey from Zurich.

Overall, I think that the Underground Lake of Saint-Léonard is definitely worth visiting if you are in the area of Sion, Sierre, or anywhere in the French-speaking region of Switzerland.


  • The Underground Lake of Saint-Léonard is located in Sierre, Valais, Switzerland.
  • Lac Souterrain de St-Léonard is the largest underground lake in Europe at 260 meters long and 29 meters wide. The largest underground lake in the world is Dragon’s Breath Cave in Namibia at 20,000 square meters.
  • Access to the lake is permitted from spring until autumn. It is closed during winter.
  • The boat ride takes 30 minutes and can be booked online at The guides speak English, French, German, and Italian.
  • The boat ride costs CHF 12 for adults and CHF 7 for children aged 5 to 15.
  • Aside from boat rides, the place can be booked for private tours and school trips.
  • There is a waiting area showing interesting information and a small refreshment area in case you are hungry or thirsty.

Related Posts: Caves

Related Posts: Excursions in Valais

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Darla Uhl is the owner of Her home is in the German-speaking part of Switzerland. Having lived almost 20 years in Switzerland, she's traveled extensively all over the country.

Darla's favorite regions to visit in Switzerland include Engadin, Lake Geneva, Bernese Oberland, Ticino, and Valais. She loves spending time with her family, hiking, visiting museums, and reading books.

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