Caves of the Mendip Hills traverse from one cave to another through the underground rivers led to the development of cave diving; the first cave dive attempt in Britain took place at Swildon's Hole in 1934. The first successful cave dive in Britain was achieved the following year at Wookey Hole Caves, where the last sump is currently the deepest in Britain at . The cave complexes at St. Dunstan's Well Catchment, Thrupe Lane Swallet, Lamb Leer and Priddy Caves have been identified as geological Site of Special Scientific Interest. There are also caves within the Cheddar Complex SSSI. A selection of the better known
Perch SSSI been recorded including a strong population of dormouse ("Muscardinus avellanarius") and five species of bat, including the Greater Horseshoe bat ("Rhinolophus ferrumequinum") and Lesser Horseshoe bat ("Rhinolophus hipposideros") which use the site for feeding. One small roost of lesser horseshoe bats is known. Both species of horseshoe bat are nationally rare. Thirty species of birds are known to breed within this site and at least 23 species of butterfly breed here. Perch SSSI The Perch () is a 72.1 hectare (178.2 acre) biological Site of Special Scientific Interest close to Cheddar Gorge in the Mendip Hills, Somerset, England. It received