An extensive system of drainage levels draining workings up to and on Masson Hill, was rediscovered in 1977 and well written up in PDMHS Bulletin Vol 8 No 2 1981. There was a lot of work done by PDMHS clearing and making accessible these workings. Also many artefacts were discovered, the ones in best condition now being on display in the museum.
The system has much 18th Century graffiti, and was photographed by myself in the early 1990s. The access is by a manhole behind the toilets at the Artists Corner car park. At one time it was possible to do a through trip from the top, however reworking of the Masson Hill quarry destroyed the Critchman workings making a through trip impossible, although I understand that some people have found a way.