Caves of the Mendip Hills Caves of the Mendip Hills The caves of the Mendip Hills are formed by the particular geology of the Mendip Hills: large areas of limestone worn away by water makes it a national centre for caving. The hills conceal the largest underground river system in Britain. The hills consist of anticlines of Carboniferous Limestone lying over Devonian Old Red Sandstone, with the sandstone exposed on the summits. When a surface stream running off the sandstone reaches the limestone it sinks below ground through a "swallet", (also known locally as a "slocker"), continuing on its way down towards sea level by
Hellfire Caves Hellfire Caves The Hellfire Caves (also known as the West Wycombe Caves) are a network of man-made chalk and flint caverns which extend a quarter of a mile (250 metres) underground. They are situated above the village of West Wycombe, at the southern edge of the Chiltern Hills near High Wycombe in Buckinghamshire, Southeast England. They were excavated between 1748 and 1752 for Francis Dashwood, 11th Baron le Despencer (2nd Baronet), founder of the Dilettanti Society and co-founder of the Hellfire Club, whose meetings were held in the caves. The caves have been operating as a tourist attraction since 1951.