Here are a couple of places in Oslo to look up.
Vigeland's park. Wonderful statues and other sculptures.
http://en.wikipedia.org/wiki/Gustav_Vigeland" rel="nofollow" target="_blank">
http://en.wikipedia.org/wiki/Gustav_VigelandHolmenkollen. The Olympic sky jump is open as a tourist attraction during the summer. The view from the top is great, and it gives you a whole nother perspective on the Olympic sport we usually only see on TV. I have a whole lot more appreciation for those athletes now.
http://www.visitnorway.com/us/" rel="nofollow" target="_blank">
http://www.visitnorway.com/us/If you ask for them I'm sure the natives will point you in the right direction. Most everyone under the age of 60 will know at least some English. When we were there the 'trik' (Street car) was reliable and dependable for getting around. And a great way to meet people. Hop on, stare and or point at a map and sound lost, someone will likely come help you. If they don't ask someone you're near for help. Ask them what to see as well.
We were there in June and in Oslo it never did get 'dark'. Even after the sun went down. The 'golden hour' was well over two hours both going down and coming up, but the golden hours weren't far apart. Further north the golden hour is even longer as the sun never really sets. I don't know how far north you're going so it you might not be seeing it all night, and youll be farther from the summer solstice, but . . . I have some decent shots from just balancing my camera on a railing and tripping the shutter, even long after sunset, and that was using ASA 200 or 400 film.
Of course the fjords along the coast will have lots of great scenery. If you can swing it, get up on the vieda, the high plains inland of the coastal mountains. Yes, we saw real live reindeer there. We started at Oslo, drove south around the southern end of Norway and up the west coast until we drove roughly straight east back to Oslo.
I took what I thought was an excessive amount of film (my last trip there wasn't all that recent) and used it all up, and ended up buying more while I was there. Every little burg we drove through seemed to have some place interesting to see or something interesting to do.
If you swim in the ocean, it will be chilly, and youll need someone watching out for jelly fish. They sting and that would be a distraction from your trip.
By the way, whats wrong with lutefisk? Its good if its prepared right. And over there you can get it prepared right, although its kind of out of season. Its a winter food.