If you haven't got much time, I'd stick to Krakow itself and ride the trains and the bash the tram network. For a break from the normal central Krakow cultural stuff, go to Nowa Huta.
Here's an extract from some Krakow guides: "In the 1950s, the Communist authorities decided to try to win over the hearts and minds of skeptical Cracovians by building this model Socialist community, just a tram ride away the Rynek Glówny. Nowa Huta, which means 'New Steelworks', was an 'ideal city'. It took up the age-old quest to build the perfect urban environment, a dream project since the Renaissance, although one that was rarely realised as few could fit the bills of those excitable architects. Nowa Huta, however, seemed like a shrewd investment to its benefactor, the goodly Comrade Stalin - the city was to be a gift to Russia's new Socialist brothers - a model for his brave new world."
The part of the Krakow tramways that is in Nowa Huta has its own 'town centre' network.