The Ballahoo Tunnels, commonly known as "Henry's Tunnel", is a two-bore tunnel situated to the east of Ballahoo, on the Main Line.
The Sodor and Mainland Railway originally attempted to cut a tunnel through the Ballahoo Ridge. However, it collapsed during construction, resulting in the railway only running trains between Ballahoo and Kirk Ronan.
After its foundation in 1915, the North Western Railway constructed its own tunnel in order to reach Vicarstown. The NWR was built as a strategic railway in a time of emergency. Speed and cheapness of construction were paramount, so a single line bore only was cut, with the Up and Down lines being gauntletted. While work was in progress, a section in the centre collapsed, leaving two tunnels (the Western - 1 mile, and the Eastern, or Henry’s - 450 yards).
The tunnel gained its nickname in 1922 after Henry refused to come out, claiming that the rain would spoil his "lovely green paint with red stripes", and was subsequently bricked up after three failed attempts to get him out. A second bore was cut alongside to provide a double line and Henry was eventually let out sometime in 1923 to help with the express. In 2011, the tunnel collapsed but was repaired in time for the unveiling of the Thin Clergyman's bust at Tidmouth.
In the first season of the television series, Henry stopped in the tunnel (like in the Railway Series). In the fourth season, the tunnel was blocked by an elephant and Henry had to take some workmen to clear it. In the thirteenth season, while painted pink, James hid in the tunnel. In the nineteenth season, Thomas hid in the tunnel from the Fat Controller after lying about an accident.