In the past this Teutonic Knights’ town was known as the Rastembork and was a base from which were organized the expeditions for Lithuania. In 1440 the town became one of the founders of the Prussian Union acting against the Teutonic Knights.
From the 14th century it was a seat of the Prosecutor of the Teutonic Knights, who built the Rastembork castle in 1360-1370. After joining the Prussian Union the Ketrzyn’s townspeople refused an obedience to the Teutonic Master and the monastic prosecutor was drowned in the nearby Mill Pond. Ketrzyn was almost totally demaged during the World War II: only the town’s walls and the 15th-century Church of St. George have survived. The Gothic Church was built on the side of the old Teutonic watch tower, destructed by the lithuanian army commanded by the princes Olgierd and Kiejstut in 1345. Despite its modest exterior, its interior hides an impressive decoration: 16th-century crystalline vaulting and 18th-century organs made by Josue Mosengel. The town (Rastembork) was renamed in 1946 in honour of the Polish national activist Wojciech Ketrzynski, who was a historian fighting with the Mazurians’ germanization. Today the castle houses a Museum presenting the memorabilia of W. Kętrzynski as well as the religious art, sculpture and porcelain of the Warmia and Mazuria region.
During the World War II the Hitler’s headquarters „The Wolfs’s Liar” was built in the nearby Gierloz forest .