Castillo de San Clemente, also known as Castillo del Món or Castillo de Perarrúa, is an 10th-11th century fortress located northwest of Perarrúa in the Ribagorça region of Aragón, Spain. Originally constructed as a Muslim fortress called Qasr Muns during the medieval frontier era, it was later adapted and maintained under Christian rule. The castle features a distinctive truncated conical tower composed of thick ashlar stonework; the structure currently stands partially divided vertically, with ruins preserving evidence of four interior floors and a semicircular-arched entrance at first-floor level. The fortress complex includes a romanesque hermitage dedicated to Saint Stephen (San Clemente), creating an important spiritual and defensive ensemble. Designated as a Cultural Heritage Site of Interest in Aragón, the castle remains accessible via a track from the village and represents significant medieval architectural heritage from the period of Christian-Muslim territorial conflict.
