We expect to arrive in Lulea from Narvik, Norway in mid August. We have several days to enjoy the train from Lulea to Stockholm. Are there any places you recommend to overnight on that journey? We will be traveling during the day as we enjoy train travel.
There are many places worth a stop along the way. You don't mention any particular interests or how many days you have, but a night in Umeå and a night in Sundsvall could be a good start. If you enjoy nature you can also add a stop in Örnsköldsvik and visit Höga kusten or Ulvön.
Sundsvall has lots of lovely Art Nouveau architecture.