Castillo de la Peña de Ayllón

Uncastillo, Spain, Spain

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Castillo de la Peña de Ayllón, overlooking the town of Uncastillo in Zaragoza province, Aragon, Spain, is a medieval fortress of Navarrese origin first documented in 921 during Sancho I's reign, later captured by Arabs under Banu Qasi and reclaimed by Sancho Garcés II in 971.

It features an oval irregular layout adapted to a rocky mound measuring 115 by 75 meters, divided into two sections with rock-hewn stairs, a southern entry gate, a central well, two towers—one 13th-century square homage tower of 10 meters with high-quality ashlars and battlements, and a slender 14th-century semi-octagonal Gothic tower linked to Pedro IV's palace with ribbed vaults and a spiral staircase.

Key in Reconquista border defense, it hosted pivotal alliances like the pre-War of the Two Pedros pact between Pedro IV, Carlos II of Navarre, and Enrique de Trastámara, before partial destruction in the Carlist Wars, now standing as evocative ruins dominating the landscape.