National Showcaves Wales

The cave was first explored in 1912 by three local brothers, Edwin, Tommy and Jeff Morgan, using candles and primitive equipment. Completely unsure of what they would discover, they armed themselves with a revolver. Edwin was the first to enter, as he was the smallest of the Morgan brothers. Initial expedition was halted at a large lake, which they later managed to cross by coracle. They eventually crossed three more lakes in the same manner, but were stopped by a tight crawl.
This squeeze, known as the Long Crawl, was first passed by Eileen Davies, a member of the South Wales Caving Club in 1963.[citation needed] The initials 'PO' were found by Eileen Davies at the pitch to Gerard Platten Hall. Peter Ogden had not descended the pitch due to lack of the required equipment and was prevented from returning by an extended period of bad weather. Exploration has been steadily continued by later cavers who have extended the cave to its present 17-kilometre (11 mi) length. Some of this length was reached by cave diving. One of these explorers was Martyn Farr, who wrote a book about the system in which he claims that the system will eventually be extended to at least 150 km (93.2 mi).
The cave was used as a filming location for the Doctor Who serial The Pirate Planet.