It's well established that hillforts were a thing in prehistoric Finland, and I think it'd be a fun addition to have them dotted around the landscape. Maybe with alloted "chiefs" that consider themselves an authority in the area, offering special quests and such. I know that the Driikiläiset fortified cities are kind of this, they are still not a straight representation of this phenomenon, which occured all throughout pre-historic Finland.
It'd be a lot to add, but just a suggestion.