The area around Charterhouse in Somerset has a long history of lead mining - believed to date back to pre-Roman times. Grebe Swallet Mine was discovered after heavy rain in July 1968 revealed a swallet (surface stream sink) in the terrain.
Fifteen years later a team of dedicated cave diigers excavted the mine and revealed its many features. These range from 18th century grafitti and miners' foorprints to an impressive 40 foot deep natural rift and galena (lead ore) deposits.
The site is securely gated (using funds given in a grant by Subterranea Britannica) but access is permitted for small groups (maximum three plus leader).