I found an interesting park while I was in Oslo and I think you should check it out as well. This park contains more than 200 sculptures which were created by a Norwegian sculptor Gustav Vigeland. All of the sculptures in this park shows us different human form in everyday situation. I love this park because I had never seen a park like this, and this was a very splendid experience to see artwork in a super huge outdoor "gallery".
The Vigeland Park (Vigelandsparken) Nobles gate 32, 0268 Oslo, Norway
However, if you do not fancy looking at these sculptures, you could still come and have a look of the park. I was here in November which I guess it was in Autumn. (Although it felt like a Winter to me...) The weather was great, and the park was beautiful. I am sure this park looks pretty in different seasons too!