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 to allow control of legal trail biking on SSSIs (where damaging to the interest), but not illegal trail biking. This loophole was closed by the Countryside and Rights of Way Act 2000 and section 19 of the Nature Conservation (Scotland) Act 2004. The process of designating a site as a Special Scientific Interest is called notification; this is followed by consultation with the site's owners and occupiers, and the notification is then confirmed or withdrawn (in whole or part). At the time of the passing of the Wildlife and Countryside Act in 1981 many SSSIs were already in existence, having