I'll second Oslo to Bergen. We did it in reverse, as part of the 'Norway in a Nutshell' itinerary which is about 12 hours (can be done over two days) because it

I'll second Oslo to Bergen. We did it in reverse, as part of the 'Norway in a Nutshell' itinerary which is about 12 hours (can be done over two days) because it replaces some of the rail journey with a fjord cruise, the Flam railway, and a mountain coach.