By Tobias Carroll To modern visitors and viewers, Stonehenge offers an air of mystery. Well, more than just an air of mystery — the ancient site has plenty of mysteries, period. Some surround its construction, while others relate to what it was used for. (There’s also the report of a UFO hovering above it.) There’s no shortage of theories about what Stonehenge was originally intended for, some of them mundane and some deeply far-fetched. If you’re after a more lived-in take on the ancient stone circle, a new exhibit at the British Museum might well be of interest. The World of Stonehenge is on…