To the north of the town are several caves of the Mendip Hills, including Thrupe Lane Swallet which is a geological Site of Special Scientific Interest (SSSI), and the St. Dunstan's Well Catchment, a cave system that includes a series of spectacularly-decorated caves totalling about of mapped passage. The caves at Fairy Cave Quarry were formed mainly by the erosive action of water beneath the water-table at considerable pressure (so called 'phreatic' development), but as the water table has fallen, many now lie well above it and the system contains a variety of cave formations (stalagmites, stalactites and calcite curtains) which in extent and preservation are among the best in Britain. Shatter Cave and Withyhill Cave are generally considered to be among the finest decorated caves in Britain in terms of sheer abundance of pure white and translucent calcite deposits. Small numbers of greater horseshoe bat (Rhinolophus ferrumequinum), lesser horseshoe bat (R. hipposideros) and Natterer's bat (Myotis nattereri) hibernate in the cave system. An area of nationally rare species-rich unimproved calcareous grassland of the Sheep's-fescue-Meadow Oat-grass type lies in the field to the east of Stoke Lane Quarry.