Some unsporting analysts suggest that the local legend that it turns around every time the nearby church tower strikes midnight may not be true. (We wondered if the local church tower is actually equipped with a bell; if not, it would make the theory rather untestable). Other even less sporting analysts suggest (here, at end) that it may even be a millstone rather than an ancient ritual megalith, but I must say I don't think you'd get very far grinding with this (also nearest river rather far down steep hill so not very practical).
Anyway, here are another couple of pictures with little U, looking a bit mutinous by the time the second was taken.
Nice day for an outing, anyway!