At least 1,100 hill forts were built in Sweden from the Bronze Age until the end of the Viking age. They were often constructed on natural hilltops from where they have a good view over the landscape. Though it is not known exactly why they were built or for whom, it's commonly believed they were used as fortified strategic settlements, temporary refuges during wartime, or as spiritual places.
The ruins of a hill fort today is mainly just wide piles of mossy stone. Since the builders used dry masonry with often rounded rocks, only few sections of actual wall remains. I imagine that the walls were originally fairly vertical and reinforced with wooden palisades. They might have had wooden gates and enough buildings to accommodate a community.
I also started a wooden bridge using the same texture.