Duero Internacional

Declared in 1998 on the Portuguese side (with its Spanish counterpart, the Arribes del Duero Nature Park), it protects a border canyon some 120 km long where the Douro quite literally marks the line between Portugal and Spain along much of its course, cutting a canyon of granite walls that shelters some of the last significant populations of cinereous vulture and golden eagle in the Iberian Peninsula — species that find ideal nesting conditions on these border cliffs, far from intensive human activity.