Picture a canal in Britain and you may well think of ducks and swans bobbing about, locks or a lovely old pub by the towpath.
But there are also more than 50 tunnels on the country’s 2,000-plus miles of waterways, ranging in length from just 25 yards to more than three miles.
The construction of tunnels to overcome geographic hurdles that were too great for locks was one of the most difficult tasks faced by canal engineers in the 18th and 19th centuries.
