If you are going to visit Poland you should start from its cultural capital Krakow, which is one of the oldest cities in Poland. The main square which is located in the city center includes Old Town, Kazimierz and the Wawel Castle. In all of those places you can find a lot of interesting information about its history.
If you love nature you should definitely go to Zakopane, the small city which is situated in the mountains. There you can enjoy the beautiful view, eat a national dishes and buy a lot of souvenirs which will make you remember this place.