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 all are derived from a standard list for that country. The ORCs/OLDs are not "banned" activities – the list includes activities which would damage the interest, but also many which might be beneficial. For example, "grazing" (a standard item on the list) would require consent, even on a chalk grassland or heathland where grazing is an essential part of management. In England (and Wales?) the list of OLDs is almost the same for each SSSI – and the list for an SSSI will only omit activities impossible on the particular SSSI (such as fishing where there is no water), and