The village of Drøbak isn't technically in Oslo, but it's such a short a way off and a lovely place to visit that it has to be highlighted. It's of historical importance too, as the German crosser Blücher was sunk in the waters here, thus delaying the invasion of Norway in 1940.
The village is dotted with wooden buildings (some dating back to the 1600s), most of them housing galleries, shops, and cafés these days.
Historically a spa town, wealthy Norwegians would come here to 'take the waters'. And if that's not enough to get you interested – Santa Claus himself lives here! You can even visit his house! 'Nuff said.