The Castle of the Warmia Chapter, erected in the mid 14th century, presents Gothic style. Nicolaus Copernicus was his most famous administrator and stayed in the castle between 1516 and 1521. On one of the walls was astronomical plaque, presumably made by himself.
Visitors can admire the constant exhibition dedicated to the Polish astronomer. Exhibits were placed in the cloister and hall where Copernicus once lived. To this day, the library collects old medical prints used by Polish astronomers.
Olsztyn Museum of Warmia and Mazury was established in 1945. His collections include collections of the region's past, such as numismatics, folk culture, history, literature, ancient and modern art, and archeology. Unique collections are given by various collections, such as the religious paintings of Warmia and Mazury, folk and linguistic works, gothic sculptures or Dutch portraits.
Castle capitol is a three-wing structure. From the east the courtyard closes the medieval Gothic wall. The oldest northern wing counts as many as four storeys and was once a representative function. There is a library in its basement and two storey cellars below it.