The most straightforward option by train would be Amsterdam-Hamburg-Copenhagen-Göteborg-Oslo. It easily takes two travel days to get to Oslo.
From Oslo you can go easily towards Bergen or Trondheim. If you take the Bergen line, make sure to at least take the train once by daytime, views are stunning.
Geirangerfjorden is a bit more challenging to get. Either you take a bus from Bergen to Ålesund, from where there will be busses to the Geiranger.
From there you can navigate by local buses again to the nearest railway line (Åndalsnes - Dombås) to get you on track to Trondheim.
Or you go all the way back from Bergen to Oslo, and get to Trondheim from there. For Geiranger you need to take buses anyway.
Nighttrains exist in Norway, and are the most comfortable ones in Europe. No Nighttrains from Norway down south to Europe. Plenty of ferries though, also overnight. With Interrail you get a discount on some of them.
A week seems a bit tight though, although you can save some time by taking overnight ferries from Copenhagen to Oslo, or somewhere from the north of Germany /Denmark. But not very familiar with those.
Check your routes on www.entur.no, although summer schedules won't be up yet.
Thank you for your quick reply!
Aaah thats why I cant really find a route yet. Do you when the summer schedule will be up?
The overnight trains/ferries is definitely something we are looking into. Question about it tho: is it included in the interrail pass?
Ferries are not included in Interrail.
Some ferry lines give a discount to passholders, this does not require a pass day to be used.
https://benefitsportal.eurail.com/?categories=1be1ba1c-80f5-4286-b255-3092f0d486cd
Aaah thank you. Very interesting how this all works!
What about trains from Hamburg up to Frederikshavn then overnight (departed just before midnight when we did it) DFDS ferry to Oslo? It’s the ferry that starts in Copenhagen with a stop to pick up passengers in Frederikshavn.
Nice journey through the Oslo fjord in the morning. Easy walk to Oslo’s main railway station from where the DFDS ferry docks. There are more and shorter ferry routes to Norway from further north in Denmark (Hirtshals) but they don’t go into Oslo.