Having fun at the mouth of the Douro river (Portugal) after a trip from Porto to Spain and back

The Douro river in Portugal is famous for its wine, Port, but it also has other wonders to offer, namely 200 km (+ 200 km return) of beautiful landscapes from Porto, by the sea, to the Spanish border, passing locks up to 35 m in height, that allow you to feel what being locked in a dungeon is, good food and easy lodging along the trip.