I'm pushing a little today with my choice for the letter I. (In my defence, may I say that 'i' isn't used much in Welsh.)
So I'm going for Iron and Industrial Revolution. The Pontcysyllte Aqueduct in North Wales is a monument to the Industrial revolution as it was one of the earliest aqueducts to use a cast iron trough. It took 10 years to build and was opened in 1805. It's 39 metres above the river Dee and carries water to Cheshire. Canal boats travel across it and there's a footpath too.
I tried to walk across it but had to turn back very quickly! Too scary. I was fine when we crossed it in the canal boat though.You see the footpath and the railings on the right of the boat in the photo and nothing on the left! It's a long way down!