Lac Souterrain de Saint-Léonard is a beautiful hidden lake waiting to be discovered within the Swiss Alps. Not many visitors to the area know about this ancient lake and cave and its surrounding area… and it’s totally worth a visit! Lac Saint-Léonard holds the title of Europe’s largest underground lake, stretching over 300 metres in length. It has crystal-clear waters that are a must-see!
Apart from the natural beauty of the lake, there are plenty of activities to enjoy. Take a guided boat tour, see the surrounding ancient rock formations and learn about the geological history of the Lac Souterrain de Saint-Léonard.
Join us as we share all you’ll need to know to enjoy this stunning Alpine lake, along with what to do and where to stay while visiting the area of Sion.
History and formation of the underground lake
Lac Souterrain de Saint-Léonard’s formation is due to the slow and steady erosion by Mother Nature. This subterranean lake was created and carved out by millions of years of persistent water flowing through the Valais Alps’ limestone rock.
The Lac St Léonard was hidden for thousands of years and was only recently discovered in 1943 by Jean-Jacques Pittard. Since its discovery, the lake has been studied by geologists and hydrologists. Many studies have been done here to understand how water and rock create caves and underwater formations. The lake opened up to the public in 1950 and since then has become a touristic landmark and site for scientific research. There are even a few legends about the underwater lake surrounded by hidden treasures by monks in the Middle Ages.
The wonders of Lac Souterrain
Lac Souterrain de Saint-Léonard has remarkably transparent water, allowing you to see deep down into the cave’s water system. The water is so clear, that you can even see the limestone formations that are submerged underwater. These limestone formations are called stalactites and stalagmites, and you can see them all around the cave.
The lake is home to a unique ecosystem of aquatic vegetation. There is sparse sunlight within the cave, so most creatures are subterranean sealife. Temperatures are relatively mild, due to a phenomenon that occurs within the cave. This microclimate allows visitors to enjoy Lac Saint-Léonard almost all year round, regardless of the weather outside.
Available tours and guided tours
Exploring Lac Souterrain de Saint-Léonard offers a truly unique experience with its guided boat tours. We highly recommend that your visit to the cave and underwater lake is planned ahead of time, as online registration is mandatory.
Boat tours:
The main attraction of the Lac Souterrain is the guided boat tour. The tour lasts about 30 minutes and will go through the cave’s interior. The guides will discuss the geological history of the lake, along with its ecosystem and legends. You can take the tour in multiple languages, including French, German, English and Italian. The boat tour costs CHF 12 for adults and CHF 7 for children aged 5 to 15. Children under 5 are free.
Large group tours:
If you are planning a trip in a larger group, personalised private tours are available. These tours can hold up to 40 people per boat and are ideal for family and school trips.
Facilities and services for visitors
Lac Souterrain de Saint-Léonard has a range of services and facilities available to you to ensure that all guests are comfortable while visiting.
There is a visitors centre where you can inquire about the lake, inquire about future tickets and register for the available tours (if you haven’t done so online). There is also a small exhibition on display.
A café is also available on-site so that you can enjoy a coffee, refreshment or small snack. Additionally, there is a souvenir shop where you can buy local momentos to remember your visit!
Lac Souterrain de Saint-Léonard is wheelchair-accessible with plenty of pathways and adapted facilities. The guided tours can also accommodate visitors who have mobility issues.
Additional activities and information about Lac Souterrain de Saint-Léonard
Apart from the guided boat tours, you can take part in special events and workshops that are organised throughout the year. They normally are about discovering the geological and historical background and conservation of the lake and cave.
Location and directions: You can find Lac Souterrain de Saint-Léonard in the municipality of Saint-Léonard, within the canton of Valais, Switzerland. To reach the cave, take a train to St-Leonard’s train station, just 1 kilometre away. From there, you can either take a taxi or walk for 10 minutes to the site. Taxis are also available at the Sion and Sierre train stations. If you’re driving, ample parking is available at Lac Souterrain de Saint-Léonard.
We recommended visiting during the weekdays and early in the morning or late afternoon to avoid peak hours. The summer months are especially busier so make sure to plan your visit.
Opening hours: The lake is open to visitors from mid-March to the end of November.
March 16th to the end of June: 10:00 AM - 5:00 PM
July to the end of August: 10:00 AM - 5:30 PM
September to November 3rd: 10:00 AM - 5:00 PM
Admission prices:
Adults: CHF 12
Group rates and discounts are available upon request.
Children (5-15 years): CHF 7
Children under 5: Free
What to wear: We suggest wearing comfortable shoes suitable for walking or wearing your hiking boots as much of the ground is uneven. The temperature inside the cave is cool all year round, so it’s a good idea to wear a light jacket or sweater and long pants.
Plan your visit to Lac Souterrain de Saint-Léonard
Visiting Lac Souterrain de Saint-Léonard is a must-do journey to one of Europe’s most captivating natural wonders.
To make the most of your trip to the Swiss Alps, book your stay with Alpvision Residences. Offering the best lodging options in the region, our various accommodations are conveniently located near the top towns, ski areas and nature reserves in the Alps. It serves as the perfect base for exploring Lac Souterrain and other nearby attractions.
