Falkirk Tunnel

The Falkirk Tunnel is 630 meters long, 18 feet wide, 19 feet high and has a 5 foot wide towpath. It passes the Union Canal under Prospect Hill in Falkirk, connecting Falkirk to the heart of Edinburgh. The tunnel was built almost 200 years ago and was originally used to transport coal. Today boaters can explore the Union Canal and eventually the Falkirk Tunnel.
The tunnel now features an improved lighting system using colorful LED and traditional white lights to highlight the Victorian engineering, contrasting with the oil lamps that originally lit the tunnel when it opened. In 2016, a programmable lighting system was installed in the tunnel. Nevertheless, the lighting conditions in the tunnel are not particularly bright, it is more of a diffuse light.
The Antonius Wall runs over the tunnel; it was part of the British Limes and the second large rampart built by the Romans in the north of Britain.

Very dark and wet - take a torch and be prepared for wet ground and some drips coming through the roof - unusual bit to walk through and worth doing though. Was a much longer tunnel than I was expecting.