A castle (from Latin castellum) is a type of fortified structure built in Europe and the Middle East during the Middle Ages by European nobility.  Usage of the term has varied over time and has been applied to structures as diverse as hill forts and country houses. Over the approximately 900 years that castles were built they took on a great many forms with many different features, although some, such as curtain walls and arrowslits, were commonplace.

Bourtzi Castle, Nafplio, GREECE
Buda Castle, Budapest, Hungary
Marienburg Castle
Edinburgh Castle
Himeji Castle
moritzburg castle
Portala Palace
windsor castle