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
Weston-in-Gordano SSSI Weston-in-Gordano SSSI Weston-in-Gordano SSSI () is a 12.55 hectare geological Site of Special Scientific Interest near the village of Weston in Gordano, North Somerset, notified in 1993. Note that there is also a separate biological and geological SSSI covering the Gordano Valley. This is a Geological Conservation Review site because temporary exposures here have shown Pleistocene sediments, including interglacial fluvial sands and marine gravels and cold-stage fluvial gravels. Rich molluscan faunas have been reported from the section. The presence of freshwater and marine interglacial deposits gives it great potential importance for the understanding of the Quaternary sequence of the Vale