The Museum of Warmia and Mazury is housed in the oldest building in the city – the Gothic Warmia Chapter Castle – and takes pride in being a unique specimen, even on a global scale.

On the wall of the cloister there is a priceless astronomical plate which was drawn in 1517 by Nicolaus Copernicus. It is the world's only surviving astronomical item made and used by the scholar. On the wall of the south wing of the castle hangs its replica, thanks to which scientists know the fate of the original. The museum also holds the Copernicus medical incunabula with his own handwritten notes, and there is a biographical exposition of the great astronomer. One should pay attention to the exhibits of archaeology, history and numismatics, ancient and modern art, crafts, literature and folk culture. The unique character of the collection is created by collections of Gothic sculpture, religious paintings of Warmia, Dutch portraits, tin and bronze casting products and contemporary graphics.

In summer time, visitors can visit the castle tower which overlooks the city landscape. The museum organizes regular projects such as “Cavata at Olsztyn Castle” and Thursdays with Copernicus.
The facility began its operation in the spring of 1945 when Hieronim Skurpski, the first city director, came along. It was first called the Mazurski Museum, and its current name was gained in 1975. Two out of seven of its branches operate in Olsztyn: the seat of the Olsztyn Daily and the Museum of Nature.
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There is free entrance to the courtyard.