A tunnel a few dozen metres long provides access to the foot of the volcano's chimney, which forms a mossy shaft of light 45 m high. You descend into the gigantic cavity formed by the gases escaping as the lava cools. Majestic vaults in beige, black (obsidian) and ochre interlock. A few siliceous concretions form milky-white jellyfish on the walls. At the far end, a lake reflects the succession of vaults