In Poland, Crakow is supposedly more fun that Warsaw, so say my Polish friends. Warsaw was pretty fun when I made a short stop there a couple years back.

Prague is one of the most interesting cities in Europe, so that's a natural stop in the Czech Republic. Nearby Praha, you have the original Budweiser brewery, Budvar. If you like beer, this is a must see.

Sweden has Stockholm which is a city I'll never get tired of. But another interesting spot is Kalmar and Ooland in the southeast.