The Kon Tiki museum and its story is something I am only vaguely familiar with, but have now learned a lot more about. It houses souvenirs and the ship from the Kon Tiki expedition. I learned a lot about the men and what they went through, but I can't say that it was the coolest thing I've ever seen.
Literally just across the street is the Fram museum, and that was significantly cooler. I still didn't know a lot about the Arctic expeditions beforehand, but exploring the ship and playing the different games (even if they were meant for someone half my age) was fun. Apparently this is Oslo's best museum, but I'm not sure if I agree. Lots of color and stuff, but lacked a variety for me. But still worth the visit if you have the chance.
The Viking Ship Museum. Was. So. Cool.
Viking longships are something I've always found interesting, but seeing them in person? More amazing and detailed than any picture could capture. They are also far larger, although the ones in the museum aren't even the biggest. I think Viking history and old Norse culture is fascinating, and I looked at every single artifact and read about it. I even bought a shirt with Viking runes on it that translates to "Man knows little."
It only made my Viking interest bigger. Highly recommend to any fellow history needs out there.