The Arandilla valley Nature · Peñaranda de Duero, Ribera del Duero, Burgos The river Arandilla comes down from the northern moorlands towards the Duero opening a narrow valley of slopes of savin and Portuguese oak, with the castle of the 10th century reformed in the 15th looking out from the hill over the houses. Photo: Rafael Tello (CC BY-SA 4.0) What to see and do in Peñaranda de Duero