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

The tunnel, No 23 in the series on the Llangollen Canal, is 421m (495 yards) long, built of brick to a semicircular section, and embraces the towpath, a recent innovation at the time. The tunnel tapers out to the S portal in the form of a parabolic arch of limestone voussoirs rising to a keystone, and set slightly proud of the high rubble-faced curved retaining wall. This wall rises to a flat string course at the base of the parapet. The cantilevered towpath has a handrail of timber on cast iron tapered supports, installed in 1822. The N portal is similar to that at the south, but the retaining wall is more sharply curved.