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
Mottisfont Bats SSSI Mottisfont Bats SSSI Mottisfont Bats SSSI () is a biological Site of Special Scientific Interest in Hampshire, notified in 2003. It is also a Special Area of Conservation. The site consists of woods around Mottisfont, which supports a population of the Barbastelle bat which is considered by Natural England to be of national importance. The site is used by the Barbastelles for breeding, roosting, commuting and feeding. It is the only known maternity roost in Hampshire and one of only six known sites in the United Kingdom as of 2002. Eight other bat species have been recorded at Mottisfont: Whiskered,