Many small/average cities are boring. However, you are close to Mazury lakes, so you can try to visit Mikołajki. About 70 km east of Olsztyn. As far as I remember city is not interesting, but I love lakes around.
Well, I loved them many years ago, I wasn't there for at least 10 years. I was told it is getting more and more crowded, but that shouldn't be problem at the moment.