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
Roman River SSSI Roman River SSSI Roman River is a biological Site of Special Scientific Interest (SSSI) south of Colchester in Essex. Two areas, Friday Wood and Donyland Wood, were formerly separate SSSIs. The site is in two separate areas. The Roman River, after which the site is named, runs along the southern boundary of both of them. There are areas of woodland, grassland, fen, scrub and heath. The woodland it mainly ancient, and there are more than a thousand species of moths and butterflies, and nearly seventy of breeding birds, including hawfinches, tree pipits and yellow wagtails. Footpaths and tracks runs through