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
Alyn Valley Woods and Alyn Gorge Caves Alyn Valley Woods and Alyn Gorge Caves Alyn Valley Woods and Alyn Gorge Caves is a Site of Special Scientific Interest on the border of Flintshire and Denbighshire in north Wales. Most of the site is also designated as the Alyn Valley Woods Special Area of Conservation and the southern part includes Loggerheads Country Park. The SSSI has an area of 190.3 hectares while the SAC covers 168.3 hectares. A large part of the site is covered by broadleaved woodland with sessile oak, ash and sycamore among the dominant tree species. Notable plants in the woods include stinking hellebore, green-flowered