Britain's biggest maze cave, accessed by a vertical shaft ("rise") in a 19th century lead mine level. The surveyed length does not include any mine levels/workings; the length comprises entirely natural passages. A full description of the cave's geomorphology and speleogenesis can be found in Cave and Karst Science, Vol. 42-1 (2015). The cave, near Alston in the Great Limestone bed of the Northern Pennines orefield, has been explored and surveyed by the Moldywarps Speleological Group.
Preceding description by Tony Harrison.
Almost all passages on the same level, created by phreatic sulphuric acid corrosion. The cave has a somewhat elevated level of radon, but only enough to become a problem with frequent, lengthy visits. The complexity can make exploration and navigation extremely difficult, and visits are usually kept short, rather than exploring the full extent of the cave.