A 121-Meter Descent Into Deep Time
On August 19, 1935, French speleologist Robert de Joly and his team descended 49 meters through a vertical shaft known locally as the "Bertras hole". They entered a sequence of colossal chambers hidden beneath the limestone plateau of Ardèche. The first, now named the Salle Robert de Joly, is immense, with ceilings reaching up to 30 meters high in a space covering 10,000 square meters. This vast void is just the beginning of a trip that takes visitors 121 meters below the surface.
The cave system is carved from limestone deposited during the Cretaceous period, over 100 million years ago. Over millennia, water infiltrated cracks in the rock, slowly dissolving the calcite and sculpting the gigantic rooms seen today. As visitors descend 700 steps through successive chambers—like the Salle du Chaos, formed by a massive ceiling collapse—they pass through a gallery of incredible mineral formations. The stable environment allows for the slow, perfect growth of countless speleothems. These calcite concretions include giant, palm-tree-like stalagmites, thin, translucent draperies, and a famous 11-meter-high formation resembling a pine cone. The descent ends in the Salle Rouge, the deepest point of the tourist path, once carved by an ancient underground river.