The express train in Sweden is called "Snabbtag" - which translates as "express train". It mainly runs on the main lines from Stockholm to Malmö
In general, there are two night trains from Stockholm to northern Sweden: The NT94 to Narvik (Norway, on the North Sea) via Kiruna and the NT94
Before my Interrail tour in the north, I only ever had two places to go: Narvik in Norway, simply because it is Narvik, the most northerly (known) city in Norway.
Does this route work in one day? As an interrailer in Scandinavia, I've always had three destinations: Stockholm in Sweden, Narvik in Norway and Helsinki