Alcoutim

The Guadiana runs slow and copper-green between two castles, one Portuguese, one Spanish, close enough to hear voices carry across the water. Alcoutim drowses in the afternoon heat, its whitewashed houses reflected in the river so perfectly you lose track of which way is up. Then someone launches off the zipline above you, crossing the international border at 70 kilometres per hour, and the spell breaks.

Alcoutim sits on the eastern edge of the Algarve where Portugal meets Spain across the Guadiana river. The town's castle dates to the 14th century, built to mirror its Spanish counterpart in Sanlúcar de Guadiana on the opposite bank. A 720-metre zipline now connects the two countries — riders launch from Spain and land in Portugal, making it the only cross-border zip wire in the world. Beyond the headline attraction, Alcoutim offers kayaking on the Guadiana, riverside beaches of coarse sand, and an unhurried pace that the coastal Algarve abandoned decades ago. The surrounding hills hold some of the region's oldest olive groves and cork oak forests, and the river yields shad and lamprey in their spring seasons.