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
Blue Anchor to Lilstock Coast SSSI the West Somerset Coast Path. Blue Anchor to Lilstock Coast SSSI Blue Anchor to Lilstock Coast SSSI ( to ) is a 742.8 hectare geological Site of Special Scientific Interest between Blue Anchor and Lilstock in Somerset, notified in 1971. It provides an outstanding series of sections through the Early Jurassic Lower Lias, spanning the Hettangian and Pliensbachian Stages and named the "Lilstock Formation". This sequence and the good Rhaetian succession beneath are repeatedly affected by faulting, making it of interest to geologists and fossil hunters. It also displays coastal geomorphology which demonstrates a particularly well-developed series of intertidal shore