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
Woodham Walter Common SSSI Woodham Walter Common SSSI Woodham Walter Common SSSI is an 80 hectare biological Site of Special Scientific Interest (SSSI) in Danbury in Essex. The site includes six nature reserves within the Danbury Ridge Nature Reserves, managed by the Essex Wildlife Trust. These are Woodham Walter Common itself, Birch Wood, Pheasanthouse Wood, Poors' Piece, Scrubs Wood and a small area in Pheasanthouse Farm. The largest part of the SSSI is the 32.3 hectare Woodham Walter Common, which is managed by the Wildlife Trust on behalf of Maldon District Council and Woodham Walter Parish Council. The site is on glacial sand and