El Castillo is the ruined edge of Cuenca's old Arab fortress, guarding the high entrance to the historic town. Little survives beyond a tower, fragments of wall, and the Arco de Bezudo, but the setting explains why Cuenca was so hard to take.
The castle later served the Inquisition and was badly damaged by French troops during the Peninsular War. Today the main reward is the walk up through the old streets and the views back over the cliffs.