The story is familiar. Nineteen maidens were caught dancing on the sabbath and were turned to stone. Their fiddler ran off and reached a neighbouring field. The pipers were clearly faster runners for they got as far as a couple of fields away, and there they stand to this day, strangely out of sight from the Maidens.
The Merry Maidens are dated to around 2,500 BC, the early Bronze Age.
The best time to visit is, of course, at one of the solstices.