The Pontcysyllte Aqueduct: a floating waterway over a Welsh valley.

Constructed from cast-iron sections supported by slender stone columns, the aqueduct resembles a narrow waterway suspended in mid-air—narrow barges still pass along it today. Thomas Telford employed cutting-edge waterproofing and metal channel technologies for the project, allowing the structure to serve for over two centuries without major modifications.

It is now a UNESCO World Heritage Site and one of Wales' most spectacular sites, where you can literally float above a vast green valley on a thin ribbon of water.