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
Debden Water SSSI has a badger sett. There are public footpaths both north and south of the stream. Debden Water SSSI Debden Water SSSI is a 20.9 hectare biological Site of Special Scientific Interest which comprises two stretches of Debden Water, a small tributary of the River Cam, and surrounding land. The site is on the eastern outskirts of Newport in Essex, where the stream joins the Cam. The flood plain of the stream has tall fen vegetation, mainly common reed, while in some areas plants such as tussock sedge and lesser pond-sedge are locally dominant. Other habitats are neutral grassland, broad-leaved woodland