A short tunnel, built on a curve, which carried the former Nantlle Railway under a road. Both portals are visible, although the south one has been partly tipped on, and are semi-circular arched and built of roughly coursed rubble, with a single row of voussoirs. Squared coursed blocks form the internal walls and roof, some up to 1.3m long. There is a gently rising gradient through the tunnel from north to south.
Site visited B.A.Malaws, RCAHMW, 26 February 1992.
(Source: taken from site notes of B.A.Malaws)
J. Hill, RCAHMW, 29.10.2003.