The film is about the adventurous explorations of the Parisian lawyer, Edouard Alfred Martel, who from 1888 to 1914 explored underground caves and canyons, an almost unknown feature of Europe at that time. Martel is considered today to be the father of speleology. Using self-made equipment, he descends the deepest chasms known at that time, crossed underground lakes and penetrated, for the first time, caves decorated with calcareous formations. The camera follows Martel’s footsteps underground in southern France where some of the grottoes he discovered are now a tourist attraction.