Bus: 30 Bygdøy from downtown Oslo to stop Bygdøynes. (Check schedules at ruter.no)
Ferry: Take the ferry Rådhusbrygge 3 by the City Hall, from SALT or from the Munch Museum to Bygdøynes. See here for schedule: https://nyc.no/
Car/bike/walk: From highway E18 or from street Bygdøy Allé, turn off to Bygdøy. Follow signs to Norwegian Maritime Museum.