The Polish-Lithuanian rulers built the rococo 'New Castle' in the mid-18th century to replace the destroyed 'Old Castle' next door. More palace than castle, it was mostly destroyed in WWII, after which the Russians rebuilt it in its current neoclassical form. These days it's an eclectic museum. The highlight is the small art collection, which includes attractive 19th-century oils and the brilliant Man with a Shovel, thought to be by Russian avant-garde master Kazimir Malevich.
Other rooms cover natural history, religion, armaments and the history of the castle.