A group of speleologist discover a cave full of concretions in the highest sea cliff in Europe. After a technically very difficult meander, they reach a large cave covered with formations of exceptional beauty and shape. While two members of the group camp , using survival equipment, the third and youngest one ventures further. Due,among other things, to the effect of carbon dioxide, he dreams of carrying out the greatest underground crossing in the world and returningtriumphant to the point of departure.