Mendip Hills to the development of cave diving in Britain. The first cave dive was attempted at Swildon's Hole in 1934, and the first successful dive was achieved the following year at Wookey Hole Caves, which has the deepest sump in Britain at 76 m (250 ft). The cave complexes at St. Dunstan's Well Catchment, Lamb Leer, and Priddy Caves have been identified as Sites of Special Scientific Interest. The deepest cave in the Mendip Hills is Charterhouse Cave with a vertical range of . Many caves in the Mendip area were excavated for archaeological and natural history studies by pioneer explorer
Wookey Hole Caves of , setting a new British Isles depth record for cave diving. This record was broken in 2008 by Polish explorer Artur Kozłowski on a dive in Pollatoomary in Ireland. During 1996–1997 water samples were collected at various points throughout the caves and showed different chemical compositions. Results showed that the location of the "Unknown Junction", from where water flows to the static sump in the 22nd chamber by a different route from the majority of the River Axe, is upstream of the sump in the 25th. There are old legends of a "witch of Wookey Hole", which are still