Jitu Cave System Nature · Onís, Oriente, Asturias Image of Onís, not of the place itself. A karst complex of shafts and galleries in the Cornión massif, in the Picos de Europa, between the concejos of Onís and Cabrales, declared a natural monument by Decree 18/2003, of 13 March; it is one of the deepest cave systems explored in Asturias. The upper entrance shaft, near the Vega de Ario refuge, is the third deepest in the Picos de Europa and ranks 38th in the world, with a main pitch of 1,135 metres; its collector ends, more than eleven hundred metres further down, in the Culiembru cave, beside the Cares river. The system has a known length of about ten kilometres, and inside it a new species of millipede, Asturasoma fowleri, has been discovered. Photo: Nicolás Boullosa from Fontainebleau, France (CC BY 2.0) What to see and do in Onís