Pilgrimage to Santiago de Compostela

[Muszla]

If you decide to walk from Puenta la Reina de Jaca to Berdun, picturesque as it is, though the way itself is much to close to the N-240, a logical direction to return to the camino GR65.3 is a narrow tarmacked coutry road signposted, I think, to Martes. Before the road crosses the Aragon river with an ugly modernised bridge there is on your left an interesting ruin. Who knows something about it?
a big a stone structure on the N bank of Aragon by the bridge between Berdun and Martes