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
Gallows Hill SSSI, Wiltshire Gallows Hill SSSI, Wiltshire Gallows Hill SSSI is a Site of Special Scientific Interest on the north side of the Ebble Valley in south Wiltshire. The area is chalk grassland and scrub which contains a number of animal and plant species that are nationally rare. The site was notified in 1965. The site includes three areas of a series of slopes with a range of aspects on a long ridge on a long ridge of Lower, Middle, and Upper Chalk formations. The site lies within the area of the Cranborne Chase and West Wiltshire Downs Area of Outstanding Natural Beauty.