@stefanmuelller Hamburg-Copenhagen, Copenhagen-Gothenburg, Gothenburg-Oslo, Oslo-Voss (all trains), then bus from Voss to Odda is probably the best way.

The Bergen line from Oslo to Voss is very beautiful, and then a 2h bus ride at the end.

Hamburg-Oslo can be done in a day if you have a fairly early start, otherwise a night in Copenhagen/Malmö/Gothenburg is a good idea.