A castle tower is a structure that is part of a castle and is typically tall and cylindrical. It is usually the tallest structure in the castle and is used to provide a vantage point for the defenders of the castle. The KEEP, which is four letters long, is the main tower of the castle and is usually the strongest and most secure part of the castle. The TURRET, which is six letters long, is a smaller tower that is usually located on the walls of the castle and is used to provide additional protection. The DONJON, also six letters long, is the innermost tower of the castle and is usually the residence of the lord or lady of the castle.