From Gardermoen (airport)
You can take the bus from the Oslo Airport (Gardermoen) to the Radisson SAS Scandinavia Hotel in Oslo, at Holbergplassen. The trip takes approx. 50 minutes. From the SAS hotel, it takes two minutes to go over and up Pilestredet to Holbergsgate. Main entrance at the corner of Sophie's gate/ Stensberggata.
From Oslo S (Central Station)
From Central Station (Airport Express / train / subway), you can go up to Stortorget (by Glasmagasinet) and take tram 11, 17 or 18 (direction Rikshospitalet or Majorstuen) to Høyskolesenteret. Tickets are cheaper when purchased in advance. It takes approx. 25 minutes walk from Central Station. Airport Express train departs from Oslo S to Gardermoen every 10 minute.
From the National Theatre
It takes approx. 15 minutes walk from National Theatre station (airport train / train / subway). Airport Express train departs from the National Theatre station to the airport every 20 minute.