Summit Tunnel, south of Todmorden near the village of Walsden, is one of the world's oldest railway tunnels. Completed in 1841 by George Stephenson's engineers, it runs for over a mile through the Pennines and carries the Calder Valley line between Yorkshire and Lancashire. When it opened it was the longest railway tunnel in the world, and its construction was a considerable feat of mid-Victorian engineering.
The tunnel portals are handsome pieces of industrial architecture in the gothic style, and the southern portal near Summit village can be viewed from public footpaths. Trains still pass through on the Leeds to Manchester line, making it a working monument to the railway age.