The Lake Winnipesaukee Mystery Stone, on permanent display at the New Hampshire Historical Society on Park Street, is one of America's most genuinely strange artefacts. Workers digging a fence post hole near Lake Winnipesaukee around 1872 turned it up, and it has been baffling scholars ever since. The stone is dark and palm-sized, intricately carved with symbols that match no known indigenous or colonial tradition, and the cleanly drilled holes through its top and bottom suggest it was made with metal tools.
It is small, and easy to miss in the museum's display case if you don't know to look for it. But it is one of those objects that, once seen, lodges in the mind. Bring up the stone at a New Hampshire dinner party and you will get one of three reactions: a shrug, a long theory, or "wait, what?"