Kemi city hall has a rooftop panorama cafe with a nice view over the city and the sea. The Sampo icebreaker is also worth visiting, although they operate only during the winter season.
The Tietomaa science centre in Oulu is more profiled towards children I think, but it was still fun to walk through. The Tähtitornin kahvila (observatory cafe) has been built atop old castle ruins in 1875 and the cafeteria has been there since 1912. And they have their own dungeon too.
