Make sure that you walk around the old town (Gamlestan). Also check out some of their historic sites and older restaurants which often have a very quaint atmosphere.
If you do get a chance to sail out into the archipelago you will be guaranteed some amazing scenery. You might also get some nice shots of hot air balloons above the city. Also check out the harbour area and I believe the Hasselblad factory has tours if you have free time during working hours.