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
Geography of Somerset Site of Special Scientific Interest (SSSI). A large number of sea bird are resident or visit the island, particularly European herring gulls "(Larus argentatus)" and Lesser black-backed gulls "(Larus fuscus)", but it is mainly preserved for its botanical interest; it is the only site in the United Kingdom where wild peonies grow. The county contains several miles wide sections of the Avon green belt area, which is primarily in place to prevent urban sprawl from the Bristol and Bath built up areas into the rural areas of North Somerset, Bath and North East Somerset, and Mendip districts in the county,