In around 1329, on a hill on the Guber river, the Teutonic knight erected a wooden fort (Rastenburg). It was raised on the charred remains of a Prussian fortified village Rast, captured by the Knights in the 13th century. Today that site is occupied by the fortified church of St George. The purpose of the fort and its crew was to defend that part of the Teutonic state against frequent Lithuanian attacks; Rastenburg was also a staging post in crusades to pagan Lithuania. The fort was twice conquered and burnt by Lithuanians, first by troops commanded by duke Olgierd in 1345, and two years later by duke Kiejstut. Each time it was reconstructed and the nearby settlement filled with new inhabitants.

The Commander of Bałga, Johan Schindekopf, granted a charter to the settlement on 11th November 1357. At around the same time the construction of a brick castle located in the south-east corner of the town's fortified walls was undertaken.

Originally the castle consisted of three wings closed to the east by a wall with a gate. The great hall contained a refectory, rooms for the Teutonic official - procurator, and a chapel. The castle was surrounded with a wall with three corner towers and a gatehouse leading to the town. The castle and the adjacent manor contained a kitchen, a brewery, a mill, a bakery, a granary, a storehouse, an armoury, a powder magazine, a chapel and a dungeon.

During the Thirteen Years' War, in 1454, the burghers overpowered the castle. They imprisoned and then executed the Order's Procurator Wolfgang Sauer. After 1525, in Ducal Prussia, the castle was turned into a seat for the local administration official known as a starosta.

At the end of January 1945, after the town had been seized by the Red Army, the castle as well as most of the old town of Kętrzyn were burnt. The castle was reconstructed in 1962-1967. The external appearance of the castle was reproduced according the19th century drawings made by C. Steinbrecht, which meant that the castle regained its Gothic style.

At present the castle houses the Wojciech Kętrzyński Museum, the Municipal Library and the Zamek Cultural Centre. The Museum collects exhibits connected with the history of the town and region. There are many arts objects, examples of craftsmanship and exhibits recording the town's history and documents from archives, which were preserved in the early post-war years by Zofia Licharowa, who organised the museum. Many historically priceless objects were saved from being damaged or dispersed. They also included parts of interior decoration in palaces and mansions near Kętrzyn, objects from damaged and looted churches, the town council's archives, and remnants of the pre-war collections of the Heimatenmuseum Rastenburg and the Prussia Museum in Königsburg.

The Museum holds three permanent exhibitions: Wojciech Ketrzyński 1838-1918, Kętrzyn-Rastenburg 19th and 20th century - a forgotten image, and Palaces and manors in the administrative district of Kętrzyn.

The castle also houses an interesting collection of Gothic sculpture, furniture of the 17th-19th century, a collection of epitaphs and funeral banners, including a child's funeral banner of three-year old Botho zu Eulenburg, dating back to 1667, which is a unique exhibit in Europe. The museum library and archives contain a rich collection of books on religious matters and a collection of documents from the former town council's archives.

In front of the castle there is a commemorative plaque, which reminds of the meeting of two Polish generals, J.H. Dąbrowski and J. Zajączek, who commanded Polish troops under the French emperor, Napoleon I Bonaparte. The generals and their soldiers arrived in Ketrzyn on 21st June 1807 after the battle at Frydland on 14th June 1807.

http://www.szlak.zamkigotyckie.org.pl/