I visited Norway but spent about 10 days there in total. We also landed at Torp and took the train to Oslo, which is pretty straightforward and quick.
Oslo is well worth a visit. A couple of days might be enough if you want to explore other places in Norway. The Fram museum and the Munch museum are both very interesting. Depending on the weather, there are also nice parks to go and spend time in.
Bergen is lovely if you get a chance to get there. There are also some lovely walks to do on the hills overlooking the town.
We also went on a hike to Preikestolen (Pulpit Rock), which is near Stavanger. It is really spectacular and great to do on a beautiful day.