Ooops, I'd been following subscribed threads & only just noticed the new Project 52.
This one's old, but for the sake of getting posting going, here's one I think I've posted elsewhere. Not strictly circles I know, but a conversation starter if nothing else:
Most people at Ollantaytambo, Peru, take photos of the Inca fortress/experimental farm. As did I, but I also snapped this from over its cliff-like edge.
Pretty pedestrian, but I like the lonely person on the wall. I've got to dig up the full-res original (not on this computer) and see if I can squeeze some decent detail out of it.