Gyfylchi Tunnel is 1015 metres long and the western end was covered by a land slip in 1947 which led to the closure of the tunnel. The eastern portal still stands high on the northern flank of the Afan valley amid surrounding forestry.

Source:
Stephen Hughes and Paul Reynolds (1989) 'A Guide to the Industrial Archaeology of the Swansea Region' Association for Industrial Archaeology.

Claire Parry, RCAHMW, 20 October 2011.