Free admission on Sun to the palace (normal price 20 PLN/4 EUR), but you still have to get a ticket, issued for a specific time of admission -- and you may have to wait a couple of hours to enter!
The interior of the Palace is worth a visit, it's beautiful... you can retrace all the King Jan III Sobiesky's life (there are audio guides in many languages including Italian and English)
Nice place to visit both day or evening. Park, lake, light show. Entry to palace at the right side, audio guide, wardrobe. And beautiful interiors inside.
A must visit place in Warsaw! Interesting on the inside ,you should pay for the full ticket which includes the entrance to palace,park & some more apartments! It's like being in another century