In Germany, April 30th is Walpurgisnacht. It was believed that on this night every witch would fly on her broom to mountaintop gatherings where they would dance nude around bonfires till dawn.
Amazingly, this night is named after St. Walpurga, a nun who came from England in the 8th century to be the abbess of a German monastery. It seems a little strange that this holy woman would have such a licentious holiday named after her. Unless of course you listen to the stories saying that a lot of early monasteries evolved from pagan colleges of priests and priestesses. More likely, the holiday happens to fall near a pagan holiday.
Remembered from a folklore book I read of my Grandfather Weikels' as a child.