Oslo has quite nice places to visit, like the Norsk Folkemuseum, a kind of Ballenberg, with a wonderful wood church (Stavkirken), built in the 12th century. At the same area one can visit also the Viking Ship Museum, with an original ship (Gokstad ship) from the 9th century.
Another nice place to visit is the Sculpture Park (Vigelandspark), with wonderful sculptures from the Norwegian sculptor Gustav Vigeland.
The Espresso House in downtown is a cute café decorated with the Scandinavian style. The chocolate cake is great! :-)