If arriving at OSL airport, you can take the airport express train all the way to Drammen Station. From there, it's only 100 metres walk to the hostel.
Drammen Hostel is a modern hostel in an old historic building. When you arrive, show up at the reception of the First Hotel Ambassadeur, which is a 4 star hotel. When staying at Drammen Hostel, you eat your breakfast at the 4 star hotel next door.