The Ffestiniog tunnel was built between 1873 and 1879 when the London and North Western Railway engineered a route to Blaenau Ffestiniog to tap the slate. The tunnel is four kilometres (two and half miles) long. The southern portal is built of rough-dressed stone, with a semicircular arch under a pediment which houses a plaque with the name of the engineer, W Smith, and the date 1879.

Source: David Gwyn & Merfyn Williams (1996) `A Guide to the Industrial Archaeology of North West Wales?. Association for Industrial Archaeology.

The tunnel lies on the Conwy Valley Line (nprn 415673).

W J Crompton, RCAHMW, 2 February 2012.