I'm flying into Bergen and plan to do the NIAN tour the next day as a one-day roundtrip, then stay overnight in Bergen so I can spend some time in the city the next day before heading to Oslo that evening either by train or plane.

I still like the idea of the train even though I'd have just finished the NIAN and its not a short ride, but would flying be the better option? It's an award ticket, so I should be able to get the flight gratis, if the times work out okay.