The 11th Dec is the final round of the national CX cup in Göteborg, (I’ll be racing), which is being held in Slottskogsvallen, by the athletics track.
This will also be the area where the MTB XC nationals will be next year, although there is no riding as such in Slottsskogen, it is only 3 KM from the area where I linked into above.
If you want to ride with the locals then simply create an account at happymtb.org and place a forum request, they are a freindly bunch and writing in English is OK.