Sos del Rey Católico retains its medieval defensive circuit almost intact — walls, towers, and the hilltop castle above the church. The castle (also called the Castillo) served as a watchtower and refuge for centuries and now provides the highest viewpoint in the town, with panoramas over the Cinco Villas comarca and the foothills of the Aragonese Pyrenees.
Walking the wall circuit takes about forty-five minutes. The path is uneven in places and the signage is minimal, which adds to rather than detracts from the experience. The castle itself is open on certain days; check locally as hours change seasonally. Even when closed, the exterior and the views from the path around it justify the climb.