Castillo de Alesga is a ruined Spanish fortress. It is situated on a hillside in San Pedro Valley near the town of San Salvador d'Alesga, in the council of Teverga, Asturias. It is situated near the Puerto de Ventana. A large square tower at its center measures about 20x. The remains of a small circular tower and a section of drywall are visible. Although the current structure is medieval, it is speculated that it was originally a Roman tower. The tower is mentioned as early as 1122. In the 15th century, it was owned by the Casa de Miranda.