Over Sierra de la Peña is located the town of Sos del Rey Católico, the county seat of Altas Cinco Villas, declared Historic Artistic Site and property of cultural interest. 
The town was set up over a hill with two natural promontories in which we find the castle and the palace and its characteristics of frontier watchtower between the kingdoms of Navarra and Aragón.
The stone houses, gothic and renaissance windows and the narrow cobbled paving streets form a harmonious monument, combined with the beautiful landscape surrounding the town.

San Esteban Church is located on the upper part of the town next to the castle’s ruins. The church from 11th century contains another church below, the so called Santa María del Perdón, or simply “the crypt”.

Sadas’ Palace
This palace was the birth place of Fernando el Católico. Worth mentioning its renaissance façade crowned with battlements and its door containing the Sadas’ coat of arms, marquises of  Campo Real. Nowadays this palace is a museum.

Uncasitllo is one of the richest monumental sets in Aragón. Declared Historic Artistic Site in 1966, the fortress that gave name to the town is nowadays one of the elements that form the whole set of the town.

This town and the fortress dates from 10th  century when king Sancho Garcés I, ruled the area.

It played an important role during 10th century, being the battlefield between Christians and Muslims.