All three of these museums are right next to one another. Viking Ship Museum. This building looks like a church from the outside, and is not marked very well with signs. It contains three actual Viking ships dug up from the ground, plus a bunch of artifacts from the Viking era. There are tours available.
Employees wear authentic cultural dress.
Vigeland Statue Park. This is a 20-acre or so park with 250 statues by Mr. Vigeland, a famous Norwegian sculptor. It's best to get a guidebook of some kind, as the park has a theme to its organization. As I understand it, Vigeland statues are not found outside of Norway. Olso has been around for a long time, and there are interesting old churches all over town.