This feature may be a level or a drainage adit associated with nearby mine shafts at Hyddgen lead mine, NPRN 303268. Its western end is fenced off for safety and partly obscured by reed and grass growth. It would appear that this is a level or adit entrance and that a gully running to the east gave access to it. A small development rock tip (NPRN 285793) some 25m to the east, close to the Afon Hyddgen, may be derived from this working. R.P. Sambrook, Trysor, 6 January 2006