Weird tree circles

I've noticed in two of the Danish towns close to where I live there are trees planted in a circle with large rocks placed under them, also in a circle. Both are fairly close to the local church or manse. I'm quite intrigued as to their purpose. Is it just a nice shady place to sit if you're out on a walk and suddenly feel tired? Maybe kids gather around to hear stories, maybe they grill sausages in the middle (hoping the trees won't catch fire)? Or maybe they are some kind of Stonehenge equivalent? Perhaps witches meet up there at night and place their cauldrons in the middle and dance in a circle with their cats. I've no idea, and I'm not sure I want to know what they are for, I think I'd rather concoct more and more outrageous stories in my head instead!