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 SSSI itself). The effect of this is to prevent development which harms the interest – except where the value of that interest is over-ridden by some more important factor, for example a requirement for a major road or port or oil pipe. The requirement for consultation covers any development which might affect the interest, not just developments within the SSSI itself – for example, a development a long way upstream of a wetland SSSI might require consultation. Note that some developments might be neutral or beneficial, even if they are within the SSSI itself – the critical point is whether