Ogof y Daren Cilau

Reed (1961) is an extremely informative early source. The entrance to the cave was discovered in 1957 by Vic Howells of the former British Nylon Spinners Caving Club of Pontypool (which was associated with the British Nylon Spinners factory in Mamhilad). Further investigation and the removal of debris showed an entrance in which a pool of water accumulated. In the ensuing period, the water was drained away and a 400 ft passage was revealed ending in a boulder choke. After decades of work and numerous cave digging projects, a connection to the nearby cave Ogof Agen Allwedd has yet to be found, even though they are only 75 m apart at their closest point.

Ogof y Daren Cilau is one of the longest cave systems in the United Kingdom (over 26 km in total) and the entrance section is long, tight and strenuous, making the trip into the further parts of the cave a serious undertaking. Because of the extent of the passages several kilometres from the entrance which would require trips of up to 20 hours to explore, some permanent underground camps have been established, including the "Restaurant at the End of the Universe", which is some thirteen hours from the entrance.