There are direct flights to Oslo from most major cities in Europe, and from some cities in North America and Asia. The three airports that service the Oslo area are: Oslo Airport at Gardermoen, Moss Rygge and Sandefjord Torp. Oslo Airport at Gardermoen is the most common, and from which it is an easy train or bus rie from the airport to BI Norwegian Business School. The airport shuttle called Flybussekspressen (Nor-Way Bussekspress and route F3 to Bekkestua) stops at Nydalen on Store Ringvei (Ring 3). It takes about 5 minutes to walk to/from BI and the bus stop. The bus takes about 40 minutes from/to the airport. The Airport Express Train to/from Oslo Central Station (Oslo S) takes 20 minutes. There is a metro (T-bane) station at Oslo Central Station (called Jernbanetorget) and lines 4 or 5 will bring you to Nydalen in about 13 minutes.
Train is a comfortable way to travel, and you can enjoy beautiful Norwegian scenery on the way. All trains to Oslo arrive at Oslo Central Station, directly in the city centre. There is a metro (T-bane) station at Oslo Central Station (called Jernbanetorget) and lines 4 or 5 will bring you to Nydalen in about 13 minutes.
Several of the public transport options in Oslo take you directly to Nydalen. Metro (T-bane) lines 4 and 5 stop at Nydalen. Bus line 37 has Nydalen as its final destination, and bus lines 30 and 55 also stop right outside the BI building. See the webpage of Ruter for more information.