Lofoten is amazing. I went there last year. Just hiking, but amazing views.
When you are in Oslo, and have time, check out Besseggen Ridge (it's a scramble). You can catch a bus to Beitostolen, maybe 4 hours, and then I think there is transport to the ferry for the hike. You can do 1 way, 8 miles, and enjoy the views Norway is famous for. I know someone there who may get more beta on how to get there. I also know someone close to Rjukan, I ice climb there, but not sure about hikes.
Another thing you can try is mountain biking on the gravel and dirt roads that are used for x ski during the winter. You can do for 100's of miles, because those trails connect.
In Oslo, take the metro to Sognsvann station, from there you can hike in the hills/forest, it's pretty. You can hike one way to another metro station, I forget the name.
I did hear about a crag in Oslo, but not sure where it is.
Let me know if you need more ideas.