Oscarshall is a small royal summer palace on the Bygdøy peninsula, built in the mid-19th century and open to visitors in season. The interiors are filled with Norwegian Romantic art, decorative painting, and period furnishings.
The palace is a useful addition to a Bygdøy museum day, especially if you want something quieter than the larger museums nearby. The surrounding park has views toward the fjord and the city.