The Hackenbeck Tunnel was cut in 1924/5, during the extension of the Branch Line from Elsbridge to Ffarquhar. As part of a deal between Sir Topham Hatt and Jabez Croarie, half the cost of the tunnel was beared by The Ffarquhar Quarry Co.; the expense of constructing a tunnel having prevented an extension being constructed earlier.
One winter, Thomas crashed into a snowdrift on the south side of the tunnel and had to be rescued by Terence. Mrs. Kyndley's Cottage is also located on the south side of the tunnel, and in the winter of 1951, Mrs. Kyndley managed to warn Thomas and his crew of a landslide that had occurred closer to the tunnel, preventing a nasty accident.
- When Hackenbeck Tunnel returned in the twenty-first season, it re-used the model of a tunnel seen the previous season, resulting in the tunnel being double tracked and having a different architectural design.