I don't really know how to find Things like that, but I'll try to remember and see if I can't find anything despite it all
Check if your university has its own sport center. They are normally cheaper than regular sports centers, and have a bunch of group lessons, where you'll meet other students.
Also check if you have an international student association or an Erasmus/ISN chapter in your city (Norway is part of the erasmus network, if I remember correctly). They sometimes also organize classes, movie evenings and weekend trips to surrounding cities. You don't have to be an international student to join, natives are also always welcome. (I only point out the international student association, because the normal student associations often mainly consistent out of stupid rituals and binge drinking, at least in D and NL).