Torca del Carlista Nature · Karrantza Harana/Valle de Carranza, Enkartazioak / Encartaciones, Bizkaia Sinkhole considered the largest in Europe and the second-largest in the world by the volume of its main chamber, located in the karst massif of Ranero. Photo: Iosu Granja/Enbata (CC BY 4.0) What to see and do in Karrantza Harana/Valle de Carranza