Arribes del Duero Natural Park is a protected area in western Spain, covering 106.105 ha in the autonomous community of Castile and León. In this area the river Duero forms the national boundary between Spain and Portugal, and the Portugal side is also protected under the figure of International Douro Natural Park. The most notable characteristics of this natural space are its biodiversity and range of watercourses, which have eroded deep valleys and vertiginous precipices. This landscape is known as Arribes, from where the reserve name come.[Source]