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
Long Dole Wood and Meadows SSSI Long Dole Wood and Meadows SSSI Long Dole Wood and Meadows SSSI () is a biological Site of Special Scientific Interest (SSSI) between the villages of Farrington Gurney and Hinton Blewitt in Bath and North East Somerset, notified in 1987. The majority of the SSSI is made up of the Hollow Marsh nature reserve run by the Somerset Wildlife Trust which covers . The site was previously called "Holly Marsh". The meadows are summer grazed, with a heath grass and sedge environment with orchids. The site is situated on the flood plain of a valley formed by a tributary of