Krakow - Wieliczka wich is the oldest salt mine. Royal Castle, market place, Old City
Warszawa- Various Museums, Palace of Culture in communist times called (For Nation of Poland from Nation of USSR) , Old City
Gdansk - Westerplatte,long market,The Sopot molo
Wroclaw - Beatufiule city imo , trade market is just smth u need to see,Hall of the century.