Upper Flood Swallet

Upper Flood Swallet which was originally known as Blackmoor Flood Swallet, is an exceptionally well-decorated cave near Charterhouse, in the carboniferous limestone of the Mendip Hills, in Somerset, England. The cave is part of the Cheddar Complex SSSI. The entrance was revealed in the Great Flood of 1968, giving the cave its name. It was dug consistently since then with breakthroughs occurring in 1971, 1972, 1985 and 2006. As of September 2008 it is over 3.5 km in length and around 125 m deep.

Cave data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).