#1 Toledo Alcázar (Toledo)
In Toledo, the Toledo Alcázar stands as a permanent sentry. This imposing 16th-century structure with four square towers has watched over the hilltop since Roman times. Once a royal palace and military fortress, it now houses the Museo del Ejército (Army Museum) and the Biblioteca de Castilla-La Mancha (Library of Castile-La Mancha).