Are you visiting Oslo this summer? Oslo can offer places to visit, like the Munch Museum, Opera House, Vigeland Sculpture Park and Holmenkollen Ski Jump. You will find more information at visitnorway.com.
At Trafikanten.no by Oslo S, you can find information about the city, maps and tickets. An overview could be found at https://ruter.no/en/buying-tickets/sales-outlets/.
You could also buy a ticket for 24 hours, or 7 days of use for the public transportation within Oslo – https://ruter.no/en/buying-tickets/tickets-and-fares/.