Garrison border town of Elvas and its fortifications, Portugal

Farmer-types take note - this 17th-century Portuguese town has the world's largest dry ditch system. It's also one of the most heavily fortified towns in Europe, thanks to the series of walls, moats and bastions that surround it.

Within Elvas, there's a number of historic churches and monasteries, including the 16th-century Church of Nossa Senhora da Assunção. The town's Amoreira Aqueduct, which has a total length of 4.5 miles, is equally impressive, comprising over 843 arches.