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
Stodmarsh SSSI numbers. Stodmarsh SSSI Stodmarsh SSSI is a biological Site of Special Scientific Interest near Stodmarsh, north-east of Canterbury in Kent. Parts of it are a Nature Conservation Review site, Grade I. a National Nature Reserve, a Ramsar internationally important wetland site, a Special Area of Conservation and a Special Protection Area under the European Union Directive on the Conservation of Wild Birds. This site has flooded gravel pits, scrub, reed beds, grassland and alder carr, with a diverse flora and fauna. Several scarce moths have been recorded and two rare birds, cetti's warbler and the bearded tit, breed in nationally