Falkirk Wheel, Scotland, United Kingdom

How the canal was routed through the wheel
The route chosen to take the Union Canal to the site of the wheel involved building a completely new section of canal, leading from the original terminus at Port Maxwell to link up with a new basin to the south of the wheel.
The water level in this basin is the same as the aqueduct at the top section of the wheel, the two being joined by the new 150 metre long Rough Castle Tunnel with elliptical cross section. This is the most recent new canal tunnel to be built in the UK since canal excavation in Dudley, West Midlands.
There are two locks to drop the canal level from that of the Union Canal to this basin. The tunnel was required because the canal had to pass underneath the route of the Antonine Wall without disturbing its archaeological remains. Just at this point the tunnel also passes below a road and the main Edinburgh to Glasgow railway line.