@Dagnar Explain.

Top Longyearbyen facts
10. Anyone can live on Svalbard. Effective since 1925, the Svalbard Treaty that defines Norway's sovereignty over the archipelago has some very interesting conditions. The most curious is that the islands are an entirely visa-free zone. This gives citizens of all treaty signatories the right to live there.

This goes a long to explaining the very diverse nature of the people living in Longyearbyen. However, this right doesn't give a ‘back door' into Norway's immigration system. Years of living on Svalbard do not count towards the time required to apply for a permanent residence permit, for example.