Covarrubias: Torreón de doña Urraca (Dona Urraca's tower)
The exterior may be visited; the interior only on occasion.
The tower looks like a four-level truncated pyramid, with solid walls and a 10th-century barrel vault. Part of the walls that once surrounded the village has been preserved. A further level, with balconies, was added in the 11th century. Elevated access with horseshoe arch. The tower is known as the Torre de Doña Urraca, since doña Urraca was buried there in 1005.
Source: Web server of Instituto de Turismo de España, TURESPAÑA.