4. Pontcysyllte Aqueduct, UK

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Source: amusingplanet.com

Constructed as far back as 1805, the Pontcysyllte Aqueduct is the longest and highest navigable aqueduct in Britain. Let me give you some perspective on that. That's a water bridge that is 307 metres long and 38 metres above the river below. The Pontcysyllte Aqueduct also happens to be a world heritage site.