In general, Alcazar means castle. The most famous is the Alcazar of Segovia.
Being the favorite residence for kings of Castilla, the Alcazar of Segovia was transformed from a small castle into an extraordinary palace. It was originally built on top of an old Arab stronghold in order to take advantage of the strategic position. Its construction began in the last quarter of the 11th century by King Alfonso VI.
In 1474 Isabel was proclaimed Queen of Castile in the Alcazar of Segovia. An artificial moat was built around the castle for increased protection, but as with most of the castle, it was altered by each king according to his likings.
The Alcazar of Segovia is a good example of Spanish Gothic architecture. A fire detroyed much of the castle's interior in the 1800's, but it has been successfully repaired for anyone to see.