Depending on what you want to see, I would reccomend the train to Bergen, and maybe Hurtigruten up to Trondheim or Trømsø.

Another alternative could be taking Hurtigruten to either Molde or Kristiansund, then renting a car getting to drive the Atlantic Ocean Road and from there continue to where you want by either car or plane - or even hurtigruten, it stops in both cities twice a day. Both KSU and MOL have direct routes to OSL (Oslo), BGO (Bergen) and TRD (Trondheim). Driving it would take about 3 hours from the Atlantic Ocean Road to Trondheim. Onwards from Trondheim, TRD is one of the bigger airports in Norway with a decent route network available.