Exploring the phosphate mines of Cloup d'Aural involves crossing lush and tropical vegetation to access the entrance of a chasm more than 98 feet (30 m) deep. This vegetation results from the presence of a tropical sea more than 170 million years ago at the current location of the Causses du Quercy. The passage of this sea facilitated the creation of a large quantity of phosphate, itself the cause of a rush of men for this natural fertilizer in the last century.