A stone and brick tunnel which carried the Nantlle Railway under the drive to Plas Dinas, approached on each side by deep cuttings, and built on curve. The tunnel is 45.10m long, 2.45m wide and approximately 1.75m high; the semi-circular arched roof is formed of three rings of brick, supported by stone rubble walls. The south portal has collapsed completely, but the north portal stands intact, measuring overall approximately 3m high and 3.8m wide, and is constructed of roughly squared blocks and rubble. The approach cuttings are 10.8m deep at the portals.
Site visited B.A.Malaws, RCAHMW, 26 February 1992.
(Source: taken from the site notes of B.A.Malaws)
J.Hill, RCAHMW, 29.10.2003.