Portugal is a small country but its landscape changes a lot going from north to the south, changing from green to yellow during the summer. This is due to the large number of rivers in the northern region when compared with the southern one and also due to the amount of water that flows in these rivers. Douro river comes from Spain and since it touches Portugal, in a region that it is the frontier between Spain and Portugal (International Douro park), it passes along the most impressive scenery that I know for a river. However, its rapids disappear due to several dams. Fortunately, most of them permit that boats pass through. The deep valleys are amazing. When the park finishes, two Unesco's World Heritage sites appear. These are the Rockart sites of the Coa valley (an affluent of Douro river) and the Douro Wine Region. These two sites may be visited from (O)Porto, 2nd largest city in Portugal, taking a train or a boat (cruise). Douro Wine Region is the oldest marked wine region and it is the mother region of Port and Douro wines.