Alcazar Segovia
The Alcázar, built like any significant castle upon a rocky crag above the confluence of two rivers, is one of Spain’s most visited tourist locations; so much so that in summer it is probably not a great idea to go there unless you like to jostle.
Originally a defensive structure, it became a royal palace, a prison, the Royal Artillery school (founded in 1762) and a military academy, being used today as a museum and military archives.
Like many Spanish castles it began life as a Roman fort, then an Arab castle until the reconquest, when in the 12th and 13th centuries it became the court of King Alfonso VIII and his English Queen Eleanor.