The ‘Balcón del Tajo’ tourist boat is a brilliant way to see the International Tagus from the inside, without breaking a sweat or moving around too much. A river cruise that plunges you straight into the biosphere reserve, between Spain and Portugal, in what is known here as the Raya.

They have two main routes: that of Cedillo-Herrera de Alcántara (2 hours, departures at 10.00 and 16.00 at weekends), where you can explore nature, history and the Spanish-Portuguese border, with an audio guide included. Or the Cedillo–Lentiscais–Castelo Branco (1-hour boat trip + bus to the Portuguese town for a self-guided tour, returning in the afternoon).

Book on their website: Cruises usually start in spring (March–April) and run until autumn. Take your binoculars along to spot vultures and storks, and wrap up warm as the river makes it rather chilly.

It couldn't be any more international.