Chirk Tunnel is a canal tunnel near Chirk, Wales. It lies on the Llangollen Canal, immediately northwards of the Chirk Aqueduct. It is 421 metres (460 yd) long and has a complete towpath inside. The tunnel is designed for a single standard narrowboat, so passing is not possible. The tunnel is straight enough to be able to see if a boat is already inside the tunnel, and boats are required to show a light. Northbound boats must maintain power and momentum in order to push through, due to the shallow, narrow nature of the canal in the tunnel (such that water has little space to pass around the displacement of the boat), and the relatively fast 2 miles per hour (3.2 km/h) southbound current of the canal. The tunnel, the tunnel portals and the canal basin are collectively a Grade II* listed str