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
Badgeworth SSSI, Gloucestershire Badgeworth SSSI, Gloucestershire Badgeworth SSSI () is a biological Site of Special Scientific Interest in Gloucestershire notified in 1954 and renotified in 1983. Part of this site () is owned and managed by the Gloucestershire Wildlife Trust as a nature reserve. There are two units of assessment. The nature reserve is unit 1 and the northerly field is unit 2. It is one of only two sites in the United Kingdom where the Adder's-tongue Spearwort ("Ranunculus ophioglossifolius") occurs; in Gloucestershire this species has acquired the name "Badgeworth buttercup" through its association with this site. The site is near the Gloucestershire