Llechwedd Slate Quarries (nprn 400426) is a major slate mine that is now worked as opencast. The quarry was started in 1846 and from 1972 the lower workings have been used as a tourist facility, allowing visitors to enter the original adit of the quarry and a series of underground chambers.
Source: David Gwyn & Merfyn Williams (1996) `A Guide to the Industrial Archaeology of North West Wales?. Association for Industrial Archaeology
RCAHMW, 18 November 2011.