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 system that is formed within the Dolomitic Conglomerate is characterised by shallow loops linking low bedding chambers, or tall narrow passages, known as 'rifts', developed by phreatic solutional enlargement of fractured rifts. The streamway in the inner part of the system formed within the limestone is characterised by deep phreatic loops reaching depths as much as , with the water flowing down-dip along bedding planes and rising up enlarged joints. In the far reaches of the cave the passages descend to below sea level. Witcombe suggests that the name "Wookey" is derived from the Celtic (Welsh) for 'cave', ""Ogo"" or