Travelling to the area of Multerland is also possible by train: the Bergensbanen. From the moment you step into the train to Bergen, on Oslo Central Station, you are in the Bergenline. It is an exciting thrilling relaxing amazing awesome journey. First of all is there the train itself: comfortable, smooth, almost soundless it is finding its way through landscapes you never saw before and you will realize that Norway is so much more than fjords. The journey from Oslo to Bergen lasts about eight hours, with some stops in between, like Lysakker, Drammen, Hønefoss, Gol, Ål, Geilo.... If you would like to eat or drink something: there is a special compartment for it, a restaurant with easy chairs in front of a window. You can enjoy the live panoramic film while you enjoy your coffee, pizza, beer or wine.
Everybody has her or his own seat number. Your ticket can be bought on internet, on their website. You will get a reference number and that is connected with the information of the conductor when he is controlling seats and passengers. He has all your internet information in his "machine", a small computer. He can see that you have payed and you will get your receipt, in case there was not a manned office on the station where you leave (like Ål).
Maybe it is even possible that you buy your ticket in your own country: employees of your country's official railroad company can tell you more.
It is also possible to buy a round trip ticket on (Gardermoen) airport at the ticket-machine or at the ticket-window. But, to avoid stress I advice not to use a ticket-window as a travel agency and to buy tickets in time on line. This avoids a sold out train, this avoids missing one of the few trains that leave from Oslo to Bergen, and you avoid stress in the people who wait in the growing queue behind you. More: wikipedia Website: NSB train travel Norway Website: NSB Bergensbanen
Video: Travelling by train from Ål to Oslo on Sunday, December 2, 2012.