Located on the edge of Aragon, in a stunning valley, built during the X-XI centuries on rock in a defensive position, initially as a signal and lookout tower. Living rooms were added to this tower, called the Tribute, perhaps with fresh water from a cistern. The polygon in front housed stays lodged state rooms and the rear was for warehouses, barns and other services. In 1516, Cardinal Cisneros ordered the demolition the exterior walls surrounding the fortress, shortening the towers, filling the moat with the stones from the battlements, the arrow-slits decommissioned and destroying the drawbridges, where now provides the access to the interior.

Today, the castle has three towers: Tower of Homage or San Miguel, the Tower of Christ in the West and Undués tower. The tall narrow keep stands out from the rest. It just has arrow-slits, and is topped by rectangular battlements. It is surrounded by a protected area.

There's also the interesting Christ Tower. It has a Gothic chapel with a walnut crucifix, 'The smiling Christ'. Carved in the fourteenth century, according to tradition it sweated blood during the difficult moments of the life of St. Francis Xavier, the last time on the day of his death. It is surrounded by a murals of great artistic interest that symbolize the Dance of Death.

The architectural framework of Javier Castle is carved in stone, and arranged provide the sense of a secure and compact structure. Next to the castle, the neo-Romanesque church was built from the same stone, to avoid destroying the harmony of the whole.

Its in good condition. In 1901 it was restored by the Dukes of Villahermosa, and become the house-museum of San Francisco Javier. You can visit St. Francis Xavier's room.

It was declared a building of public interest in the Cultural Foral Decree of 2 February 1994. It is also protected by a Spanish Historical Heritage Decree of April 22, 1949, and Law 16/1985.