The site of the north east 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 November 1999, the portal was not visible (only a section of stone walling above the arch could be seen) but it was believed to lie under spoil tipping.
RCAHMW, 06 November 2007.