"Henry's Tunnel" is the nickname given to the tunnel on the Main Line near Ballahoo. It got its name after Henry was abandoned there in 1922, claiming he did not want the rain to spoil his "lovely green paint with red stripes".
In the Railway Series, Henry's Tunnel was originally single-bored until Henry was bricked up inside it and a second tunnel was bored alongside.
- The tunnel's number of tracks changed every time it appeared up to the eighth season. In the first and fourth seasons, there was a tunnel bore with two tracks and a tunnel bore with one track. The tunnel didn't appear again until the seventh season, when each bore had one track. Then in the eighth season, both bores had two tracks and the tunnels have stayed that way since.
- In Thomas and the Magic Railroad, the tracks leading to the bores were curved, there was a track above the tunnel, and a siding and a water tower were outside one of the bores.
- A signal box and water tower has appeared and disappeared at the portal since the seventh season.