Sos del Rey Católico

The town's position on a rocky rise made it a natural stronghold, and after the Reconquista it served for centuries as a frontier post between competing kingdoms. Ramiro I brought it into the Kingdom of Aragon in 1044. It was named capital of the Cinco Villas region in 1711.

In January 2016 it was admitted to the association of Spain's most beautiful villages.

The church of San Esteban stands next to the castle and is the town's most layered monument — church, crypt, and cloister together, with the cloister giving access from the main square up to the church's principal doorway. The crypt holds the chapel of Santa María del Perdón and several other chapels, along with stonemasons' marks carved into the walls.

Above everything sits the Castillo de la Peña Felizana. Originally a timber fort built to hold the frontier between Navarre and Aragon, it was gradually rebuilt in stone as construction techniques advanced. The most significant surviving element is the restored Torre del Homenaje.

Down in the town, the Palacio de los Sada is a stone ashlar palace from the late medieval period, identifiable by the family coat of arms above the entrance. It was here that Queen Juana gave birth to the future Ferdinand II, who would become Ferdinand of Aragon. The palace now functions as an interpretation centre devoted to Ferdinand's life and era, using panels and audiovisuals, and also houses the municipal tourism office, which organises guided visits.

The Renaissance Casa de la Villa has served as the town's administrative seat since the council built it in the late medieval period, restored most recently in the 1980s. The Palacio Español de Niño on Calle Mayor is another Renaissance building, notable for its arched upper gallery, a studded archway entrance, and a patio floor made of a river-stone mosaic. The Colegio Isidoro Gil de Jaz on the main square follows the Aragonese style, with four floors and a top gallery of semicircular arches.

The medieval Lonja was built as a market and council meeting place. Its main building is now the municipal library, and its open portico of pointed arches still stands. Two pits carved into the floor for storing ice remain visible.