Pontcysyllte Aqueduct

Pontcysyllte carries the Llangollen Canal across the River Dee in Wales 39 meters above the river, and you can cross it on foot or by boat. Completed in 1805 after ten years of design and construction by William Jessop and Thomas Telford, it is billed as the tallest navigable aqueduct in the world, and it was inscribed with its canal as a World Heritage Site in 2009. Walk the towpath that runs along one side of the water channel: the drop on one side and the canal on the other, with only a railing between you and the valley, says more about the nerve behind the design than any figure. Boat trips along the canal start nearby at Trevor Basin.