Another very nice place to have lunch: on our way from Gol to Asker (near Oslo) we stopped at Baerums Verk and had a good pizza at Kokeliko. 
To visit Oslo, we had chosen an Airbnb in Asker and this was a good choice: it was a very spacious and modern apartment in a suburb of Asker, which has a train station with frequent trains to Oslo. Parking your car is easier in such a town, and after two weeks in quiet nature, we discovered that we didn’t enjoy Oslo city center: so many people! In 2014, I had had a great time in Oslo, so this is not about the city, this was about us, we had gotten used to the quietness and solitude and liked to keep it that way a little longer.
In Oslo, we visited the Kon-Tiki museum (about the adventures and research of Thor Heyerdahl) which I loved! It has the original raft. The Fram museum next door (about polar expeditions) also has the original ship named Fram. This museum was also very interesting, you can walk on the ship, it’s fascinating that this ship has been in all these places with people like Nansen on it. A downside of the Fram museum is that it’s very busy (on Tripadvisor it’s listed as Oslo’s top attraction). So I recommend starting at the Fram museum and then visiting Kon-Tiki.
Walking around Oslo we passed the statue of Gunnar Sönsteby, a prominent member of Norway’s resistance in World War II. 
We had purchased an Oslo Pass, but decided that this one day in Oslo was enough for us: we wanted to continue hiking in nature. So the next day, we drove to Stein Gard to walk the two Kolsastoppen. This was quite an easy walk, on beautiful paths and the view on Oslo Fjord is nice.
The day after that, we found a walk near Asker: around Semsvannet lake. This was a very easy and relaxing walk compared to our previous hikes on this holiday.
And that was it. On september 14 we drove from Oslo to Kristiansand (again a nice lunch: at Bökekroa in Larvik). We had planned a walk at Odderöya, but it was pouring. Next time maybe. Spent our last kroner eating a pizza, and the next morning got on the ferry to Hirtshals, where we arrived around noon. We had hoped to drive all the way home in one day, but got stuck in traffic in Denmark, passed Hamburg around 19:00 and were exhausted, so we found a hotel near Bremen which, according to reviews, had comfortable beds. This was an excellent choice: we slept like babies and after a good breakfast, were ready to drive home.