Marble Showers in Ogof Fynnon Ddu, South Wales

Ogof Fynnon Ddu (Cave of the Black Spring) in South Wales is one of the UK's longest cave systems and offers a fabulous trip which more or less tracks it's stream from where it sinks into the hillside, to it's resurgence some 300 vertical metres below.
This particular part of the cave is known as Marble Showers, for it's distinctive patterned walls. It really is quite spectacular, with an impressive stream which holds deep holes to dunk unwary cavers!