At the foot of the cliff, ranging in altitude between 98 and 40 metres, there is a large natural underground cave with caverns displaying many stalagmites and stalactites, draperies and columns. It was opened to the public in 1950, but can only be visited with specialized guides.
Evidence of prehistoric human inhabitants has been found in the cave. There is a museum of Prehistoric Anthropology within the Exotic Garden displaying many of those prehistoric remains. It was founded by Prince Albert I in 1902.