Olsztyn is the capital of Warmia and Masuria, a city of lakes and a brick castle where Copernicus once served as administrator. The old town is small: market square, high gate, cathedral, and parkland that quickly turns into lake shore.
It is the usual starting point for the Masurian lakes rather than a monument-heavy destination in itself. Forests and water are never far from the centre. A transfer from Gdańsk drops you into lake country without the train changes.