Kętrzyn Castle is a Gothic building erected in the second half of the 14th century. The castle was built in a shape of square. Initially it had three wings built around a courtyard. It was surrounded by a defensive wall with three towers and an entrance gate from the town side. In the northern wing there was a refectory, chapel and apartments of the main Teutonic official. The castle and the farm that adjoined it housed, among others: a kitchen, a brewery, a mill, a bakery, a granary, a pantry, an armoury, a powder magazine, a chapel, and a prison. Currently, the castle houses the Municipal Library and the Regional Museum. The basement of the northern wing is a house of a knight brotherhood. The museum's collection includes, among others a collection of paintings, sculptures and antique furniture from the 15th to 19th centuries.