Warsaw and Krakow are both amazing and full of historical sites. Are you looking for specific places to visit in those cities, or other cities to explore? Gdansk is interesting, Zakopane is beuatiful - but really between Warsaw and Krakow you could easily fill a few weeks without running out of things to do, especially if you take a day to see Auchwitz, the salt mines (also a popular day trip from Krakow), if you are interested in Holocaust history, there are Treblinka tours out of Warsaw. The old Jewish cemetery, the Jewish ghetto, the Schindler factor, Wawel Castle…There’s quite a bit to do for any history buff.