Tidmouth Tunnel, also known as the Castle Tunnel, is a tunnel on Duck's Branch Line between Tidmouth and Tidmouth Hault.
It first appeared in the third season and made numerous appearances until the ninth. The architectural style changed in the later seasons. Although never mentioned by name in an episode, it was first named in an eighth season learning segment. It returned in Tale of the Brave in the same architectural style as the third season and later appeared in The Adventure Begins and has made infrequent appearances since.
In the television series, this is where James once tried smoking bees off his boiler.
- Season 3 - Buzz, Buzz, All at Sea, Tender Engines (deleted scene), Oliver Owns Up and Percy, James and the Fruitful Day
- Season 7 - Emily's New Coaches, Bill, Ben and Fergus (deleted scene), Edward's Brass Band, James and the Queen of Sodor (stock footage), The Spotless Record, Snow Engine, Something Fishy and Best Dressed Engine
- Season 8 - Percy's New Whistle (stock footage)
- Season 9 - Molly's Special Special
- Season 19 - A Cranky Christmas
- Season 20 - The Missing Breakdown Train
- Tidmouth Tunnel has had numerous modifications throughout the years:
- Season 7:
- The tunnel's architecture changed.
- The lake became significantly smaller.
- Season 9:
- The lake beside the track disappeared and replaced with grass.
- Tale of the Brave:
- The tunnels architecture returned to its original design.
- The lake returned to how it was in the third season.
- The number of tracks leading through the tunnel changes between one to three tracks on many occasions. Since Tale of the Brave, there have been two tracks.
- The Castlelated Tunnel is a modified version of this tunnel.