Oslo has so much to see unfortunately on our one week vacation we couldn't get to see it all but my favourite locations we visited Where the Norwegian Museum of Science and Technology, My favourite was the science section which had information about natural sciences and technology and future technology. They showed Robots in the Robot Centre which was very cool to see and interact with as I've never seen one in person, the amount of work that was put in building them was phenomenal.
We saw the famous Oslo Opera House; the views are incredible on the rooftop being one of the main tourist sites in Oslo which is well worth the visit.
It's free so you can't turn it down; from a distance the building itself looks like a ski slope. Most people go there to watch the opera but the views on top of the building are amazing with a great panoramic view of the whole of Oslo and river, when we was there it was the summer so the weather was nice and hot.
If looking for a nice day out with the kids the Vigeland Park was great, we grabbed some food and blankets and just relaxed on the grass. The park is located on the North-West of Oslo so you can get there by tram, once arriving you will defiantly have a relaxing time inside, the park itself has beautiful scenery and breathless artworks.