The Olsztyn Castle, officially the Castle of Warmian Cathedral Chapter in Olsztyn, is a Brick Gothic castle located in the heart of Olsztyn, in northern Poland. Built in the 14th century, it served as the seat for administrators of property of the Warmian Cathedral Chapter. The most well-known administrator caretaker was Nicolaus Copernicus, a canon of Warmian Cathedral Chapter in Frombork, who resided here between 1516 and 1521. The largest expository room is the refectory with a diamond vault built around 1520. Currently, the castle houses the Museum of the Warmian-Masurian Voivodeship.

Olsztyn is a city on the Łyna River in northern Poland. It is the capital of the Warmian-Masurian Voivodeship, and is a city with county rights. The population of the city was estimated at 169,793 residents in 2021.