There's nothing special about the palace actually, just a couple of rooms with some exhibits...the park where it's situated seems more interesting, you can have a good time walking and watching some statues and monuments or simply enjoying the nature.

I stumbled across this park by accident, looking for the Wilanow Palace and totally mis-reading my map! Krolikarnia is only about 30 minutes walk from the Start hotels complex in Warsaw's Wilanow suburb, and so on a hot day is well worth a visit. Sunbathing in swimming costume all over the small but attractive park on a Sunday appears to be de rigeur! There is a very nice cafe in the palace building, with chairs and tables outside too, although the look of the rather forbidding staff inside the palace dissuaded me from entering, so I can't relate what it's like inside.