Tags: Cave.
Ogof Draenen (Welsh for Hawthorn Cave) is at 66 km (official figure; the true length of passage is still being revised upward with a rough modern approximation at it being 70 km) the longest cave system in Wales and the second longest in Great Britain behind the Easegill System Lost Johns and Notts 2 system in North Yorkshire.The cave was known only as a small entrance on a steep hillside until several years of digging broke through into major passage development in October 1994.