Grottes du Cerdon

Grottes du Cerdon is an underground cave system in the commune of Labalme, in the Ain department, within the Bugey area of the Auvergne-Rhône-Alpes region of France. The caves open into a rocky hillside above the Cerdon valley, close to Lake Nantua and the Ain river, surrounded by steep vineyard slopes. Combining a natural cave walk with a themed prehistoric leisure park, it ranks among the region's most visited underground sites.

What does the cave tour look like?

The visit follows the course of a vanished underground river that spent millennia carving a network of galleries through the limestone. The path feels more like a short hike than a museum stroll: it descends via several hundred steps, with a total elevation change of over a hundred metres. A standard visit takes roughly 45 minutes to an hour, while the extended route runs closer to ninety minutes. The tour ends at a dramatic natural rock archway — the point where the ancient river once resurfaced — opening onto a viewing platform set into a cliff face above the Cerdon valley. Visitors who want more can continue on to a belvedere with sweeping views over the valley and its vineyards.

Where do the cave formations come from?

Inside, the galleries display a full range of calcite formations: stalactites, stalagmites, floor-to-ceiling columns, and thin, wavy draperies clinging to the walls. A distinctive feature here is the presence of gours — small rimstone dams built up where water trickles over uneven cave floors, forming stepped, terraced pools that cascade one into the next. These range from a few millimetres to several metres across and took shape over thousands of years as dissolved limestone slowly precipitated out of seeping water. The rock itself is marine limestone laid down during the Jurassic period and later uplifted once the ancient sea retreated.

What is the history behind the site?

Traces of human presence near the caves date back more than fifteen thousand years, and that prehistoric occupation is what inspired the leisure park built alongside the cave entrance. Centuries later, during the French Revolution, the cave interior was pressed into service for gunpowder production, and in the 1920s its steady temperature and humidity made it a natural spot for ageing Bleu de Gex cheese. Today the site serves purely as a visitor attraction.

What else is there to do besides the cave?

At the cave entrance, a prehistoric-themed leisure park welcomes families with children from age four upward. Activities recreate ancient skills: pottery shaping, ochre painting, fire-starting with traditional tools, spear-throwing with an atlatl, jewellery making, and simulated archaeological digs. Together, the cave and park make for a full day out combining an underground adventure with hands-on activities above ground.

FAQ

How long does the cave visit take? The standard route takes about 45 minutes to an hour; the extended version with the belvedere detour runs around ninety minutes.

Is the walk difficult? The path involves several hundred steps and feels like a light hike, so it's generally recommended for children from around age 7 or 8 upward.

What can visitors see inside? Stalactites, stalagmites, columns, calcite draperies, and gours — the terraced rimstone pools formed by flowing, mineral-rich water.

Are there other attractions nearby? Yes — a prehistoric leisure park sits right at the cave entrance, and the surrounding area includes the Ain river valley and the vineyards of Cerdon.

When is the site open? The caves operate seasonally, roughly from spring through autumn; it's worth checking current opening dates and hours before visiting.