Constructed between 1795 and 1805, and said to be Telford’s most impressive work, Pontcysyllte Aqueduct was built to carry the Llangollen Canal across the Dee Valley.

It’s an alarming 126 feet high and a staggering 1007 feet long, which makes it the longest and highest cast-iron aqueduct in the world. Today it’s a protected Grade I listed building and a Welsh National Monument. And it’s still crossed by more than a thousand canal boats a year, by motorised or horse-drawn boat, and for the really very brave, on foot (it forms part of the Offa’s Dyke National Trail). Whichever way you choose to cross it be warned: those with a delicate nature probably shouldn’t look down.

www.pontcysyllte.co.uk