Train from Oslo to Bergen, Norway

If you haven't already purchased your train tickets, the best suggestion I have is to not take the direct train ride (though much of it is very scenic), but to divert somewhat from that to follow the classic Norway-in-a-Nutshell route from Myrdal to Flam to Gudvangen to Voss in lieu of the segment of the train trip between Myrdal and Voss. The NiN route makes for a rather long day, but it is massively scenic. It's no problem making the connections between the various modes of transportation, assuming the departures you need are not sold out--which they might be.

It's cheapest to buy the components of the trip yourself, but the company NorwaysBest sells packages (at a markup). It's possible you can find all the schedules on its website so you can figure out the best timing for you and then check on whether tickets are still available for all the trip segments.

Thanks so much for the suggestion!!! I will check this out.

Seats on the left side of the train have a better view. Be sure it'll be light out for most of the ride. Enjoy!

Yes--Daylight is important. So is not having a seriously rainy, foggy day--but that is, sadly, not predictable.

I think the least scenic part of the trip is the last bit, between Voss and Bergen, so I'd focus on getting the rest of the route done before dark--which will of course be very late in June.