Kętrzyn – Polish city situated in the Warmian-Masurian Voivodeship. Its current name was assigned in 1946 in honor of the Polish historian Wojciech Mentsynskoho. Before the Second world war kętrzyn wore German name of Rustenberg.

In the fourteenth century on the territory of modern Kętrzyn was built as a defensive fortress of the Teutonic order, which is already in 1311 tried to besiege the Lithuanian Prince. In the thirties of the fourteenth century began the construction of wooden posts, which was later replaced by a stone castle. Gradually the settlement was surrounded by 13 defensive towers, two gates were built. The construction of the castle contributed to the rapid economic development of Kętrzyn, which received city rights on 11 November 1357.

Kętrzyn and the surrounding area took an active part in the hostilities, the First and Second world wars. During the Second world war in the forests East of Kętrzyn was built as the headquarters of Hitler's "Wolf's lair". The bombing of 1942 and the battles of 1945 led to serious destruction of the city. Old town and castle were burned by the soldiers of the red Army. The total number of destruction has reached 40%.

In 1946 the city was included in the newly-formed province of Olsztyn. The German-speaking population was deported to Germany. The city's name was changed on 7 may 1946.

Despite the severe destruction, in kętrzyn preserved many monuments and other sights that attract many tourists. In Gothic Teutonic castle houses the Museum and the city library, cultural events and music concerts. Among the religious monuments, the most valuable is, perhaps, the Gothic Basilica of St. George and St. John's Lutheran Church.