Medieval Japanese castles were mainly built out of wood. You can see this if you visit one of the surviving castles in Japan. However, the newer reconstructions of the Japanese castles are now made out of concrete and have much more modern interiors.
Castle Tower: Also know as castle keep. It is probably the most important part of a castle and is defended the best. A castle tower is used as an observation tower, a place for the governor or a Daimyo to stay and also a place to refuge in case of a siege.
Guard Tower: Used as watch towers and also used as storage rooms. They are normally placed in the corners of a Japanese castle.
Wall and Moat: These are used to defend the castle and everyone inside.
Gate: A typical Japanese castle normally has two gates which are greatly defended.
Stone Drop Window: They are used to throw stones and hot liquid on attackers.
Arrow Slit: They are used to fire arrows out of.