Viking Ship Museum - Museum with historic viking artifacts and wooden ships. Located outside the city, bus is the best way to get there.
Royal Palace - Situated atop a hill near the city centre, it’s a great place to overlook the city and harbour and to take photographs.
Akershus Fortress - Medieval castle on the shoreline. Interesting to walk around and see the artifacts. Oslo has many historic buildings; this one protected the city.
Couchsurfing near Oslo Central Station/Opera House (pictured below) - I tried the app Couchsurfing for the first time. Free accommodation, where you interact with your host. Definitely worth the saved money, as Oslo is one of the most expensive cities out there.
N/A - I didn’t really go out much in Oslo. My host cooked me an Indian meal, and the rest I brought from Varberg’s supermarket.