 Except after periods of heavy rain, the river bed is largely dry downstream of Ystradfellte, the river only rising to the surface again just before the cave.The cave has been known to humans for many centuries , as it is not easily overlooked once one is in the valley, but because of the passageway's susceptibility to severe flooding there has been no evidence found of any prehistoric human habitation.The cave and its many visible fossils were mentioned in the writings of Edward Lhuyd, and in the 19th century it was mentioned again by the first pioneers of caving.