Bridge of Gradefes sobre el Esla Monument · Gradefes, Tierras de León, León The work of the engineer Bienvenido Oliver, carried out in 1920, one of the first examples in Spain of a structure of reinforced concrete pontoons with hinges in the arches, an uncommon technical experiment in a rural setting. Photo: LOBO QUIRCE (CC BY-SA 4.0) What to see and do in Gradefes