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
Site of Special Scientific Interest they harm the interest features. The owners and occupiers of SSSIs are required (Scotland, England, Wales) to obtain consent from the relevant nature conservation body if they want to carry out, cause or permit to be carried out within the SSSI any of the activities listed in the notification. Formerly these activities were called 'potentially damaging operations' or PDOs. Under the current legal arrangements they are called 'operations requiring consent' or ORCs (Scotland), or 'operations likely to damage the SSSI interest' or OLDs (England & Wales?). The list of ORCs/OLDs for each SSSI is unique to that site – though