The Tatra Mountains lie partly in Poland and partly in Slovakia, marking the border between the two countries. 
The most beautiful city in Poland, in my opinion: Krakow has to be seen. It's stamped with charm. Visiting its large square in the city centre allows you to jump back in time.
This is where the Auschwitz-Birkenau extermination camp was built. A free shuttle bus leaves the town of Auschwitz (located roughly two miles away) every 30 minutes.