Pwll Du tunnel, 1875m (2050 yards) long, was probably made from the northwards extension to Pwll Du in 1815 of a mining level in the hillside north of Blaenavon Ironworks (nprn 34134). It carried Hill's Tramroad (nprn 85860) through the high ground to the north of Blaenavon. There is a single portal at the southern end (nprn 85831) and two portals (nprn 34976 and 91754) at the northern end: the more westerly carried the tramroad between the Ironworks and Tyla quarries and that to the east, probably dating from 1816, carried a line to Garnddyrys Forge (nprn 34137) and the Brecknock and Abergavenny Canal, with a junction just inside the tunnel.
RCAHMW, 06 November 2007.