The Pontcysyllte Aqueduct carries the Llangollen Canal over the valley of the River Dee, east of Llangollen in north Wales. The aqueduct is 307 metres long and it is constructed of cast iron troughs mounted on 19 masonry arches that carry the canal 38 metres above the river (note a narrowboat on the aqueduct). It was built by Thomas Telford and it was opened on 26 November 1805. Today it is a World Heritage Site.
Canals, UNESCO, Bridges - Aqueducts
Links: en.wikipedia.org, news.bbc.co.uk