Chirk Tunnel, including the N and S Portals, and Chirk Basin.

Chirk Tunnel, which includes the northern and southern portals and Chirk Basin, is a significant structure on the Llangollen Canal, built in the early 19th century. The tunnel is 421 meters (495 yards) long and constructed from brick in a semicircular shape, featuring a towpath that was a new addition at the time of its construction. The southern portal of the tunnel has a parabolic arch made of limestone voussoirs, which rises to a keystone and is set slightly proud of a high rubble-faced curved retaining wall. This wall extends to a flat string course at the base of the parapet. The cantilevered towpath, which includes a timber handrail supported by tapered cast iron supports, was installed in 1822. The northern portal mirrors the southern one, but its retaining wall has a sharper curve.