The largest caves in the Cheddar catchment occur along the southern side of Blackdown, around Charterhouse. These caves, GB Cave, Charterhouse Cave, Longwood Swallet, Manor Farm Swallet and the recently extended Upper Flood Swallet are classic examples of swallet caves. Relative to their size, this group of caves, especially GB Cave, are some of the most intensively studied in the world. All five major caves are similar with streamways, often well decorated with stalagmites, descending down to a sump or a choke, with up to four tiers of relict high-level phreatic passages.
The caves drain to Cheddar Risings. Above these large springs at the mouth of Cheddar Gorge there is a complex series of abandoned caves. The largest is Gough’s Cave, 2.1 km long, which intercepts the underground River Yeo, which has been followed upstream through several deep sumps.