Book your Eurostar(s) as soon as you know which one you want to use because pass holder seats are limited.

First tip get a reservation for BRU- Cologne on ICE 

Secondly make sure Eurostar is also available for your dates as reservations for pass holders are limited.

Thirdly make sure you understand the in/out days as you can travel to and from Eurostar terminal on UK trains on the day. I travel from Leeds and pick up lunchtime E*.

Others will advise on Scandinavia. 

Thanks guys,

Eurostar is a waste of time trying to get an Interrail ticket, we even got to speech with  a Eurostar help desk and he said we were wasting our time, so we splashed out and bought them !

thanks for the ICE info.

I must admit to the same next Easter, we got a second class to Bru not much more than the first class reservation.

Forgot to suggest first class if you have the budget. I know Norway doesn't  have first class as such but apparently has a premium section.

Currently finishing a trip from Nice to Lille in first. 8 hours relative space and quiet

That entirely depends on when you want to travel and how long in advance you can book. Now that summer is over, availability seems to be much better again. E.g. there are still seats London - Brussels tomorrow.

When are you planning to travel?

The tickets/reservations for Swedish trains after the 10th of December will most likely be available not before mid November. 

seat61.com has best overall info aimed at mainly Brits-or those who are used to and cannot even think of other ways. It is NOT specific for passes, but for normal ticketing and not ultra-low-budget.

From Narvik south via Norge requires a payable BUS-till Fauske (where it connects to the trainline south to Trondheim. They may give a discount-but even then NO is horrendously expensive for about everything a normal tourist needs.

In winter be aware (many completely forget this) that it is really dark there=24 hrs night, around 21/12. Around 12/13 hr it gets a little lighter and that may last for maybe 1 hr. But even south NO or mid-SE has only 2-3 hrs of barely daylight then.

There is no discount anymore.

You need to reserve on the trains to Trondheim and the one onto Oslo. Entur can do these by email you just need to call them. Reservations are free if you have 1st class pass.

You need to call them