Chirk Tunnel is a canal tunnel near Chirk, Wales.
It lies on the Llangollen Canal, immediately northwards of the Chirk Aqueduct. It is 459 yards (420 m) long and has a complete towpath inside. The tunnel is designed for a single standard narrowboat, so passing is not possible. Fortunately the tunnel is straight enough to be able to see if a boat is already inside the tunnel.
This tunnel was the first tunnel in Britain to have a towpath in the tunnel (along with its shorter neighbour - Whitehouse Tunnel)
Sources of Information
-  Wikipedia