The 1,248-foot-long Glenfinnan Viaduct was a genuine wonder when it was built in 1897, and remains so today. The railway's contractor, Robert MacAlpine (known among locals as "Concrete Bob") pioneered the use of concrete for bridges when his company built the Mallaig extension, which opened in 1901. In more recent times the viaduct became famous for its appearance in the Harry Potter films. The viaduct can be seen on foot; about half a mile west of the railway station
in Glenfinnan, on the A380 road, is a small parking lot. Take the footpath from here; you'll reach the viaduct in about ½ mile.
A380, Glenfinnan, PH37 4LT, Scotland