Krakow is a really great place, I went there earlier this year to watch Fulham play and had a great time. Salt Mines were something else (they have a huge Cathedral 200 metres underground, google for more info) and Auschwitz is only about 90 minutes way too, which I think everyone should see once in their life.
City is really great place for chilling out and it's really cheap for food and drink. The Jewish quarter is the best place to drink at night.
