The north portal of Pwll Du tunnel (nprn 85830), carrying Hill's Tramroad (nprn 85860) between Blaenavon Ironworks and Tyla Quarries, Garnddyrys Forge and the Brecknock and Abergavenny Canal, lies immediately north of and below a minor road. In January 1992 the portal was observed as walled up and partly tipped over, with only a single ring of segmental stones forming a semi-circular arch and a small part of the flanking stonework visible.
RCAHMW, 06 November 2007.