The Glenfinnan Viaduct was built between 1897-1901. Located in Glenfinnan, in the West Highlands of Scotland, it forms an integral part of the world-famous West Highland Line. The 21-arch viaduct was one of the largest engineering undertakings using concrete when it was built by Sir Robert McAlpine (who earned the nickname "Concrete Bob.")

The West Highland Line connects Fort William and Mallaig, and was a crucial vein for the local fishing industry and the highlands economy in general, which suffered enormously after the Highland Clearances of the late 1800s. Nowadays, the trains that cross are usually pulled by diesel locomotives, but in the summer, the Jacobite steam train operates, which runs a heritage service using steam trains . It is a popular tourist event in the area, and the viaduct is one of the major drawing cards for the line.

The Glenfinnan Viaduct recently came to prominence in the Harry Potter film Harry Potter and the Chamber of Secrets, the second in the series, when the Jacobite Steam Train became transformed into the Hogwarts Express and was filmed crossing the viaduct.