We happened to be in Copenhagen for the celebration of "Midsummer's Eve".  Linked to the summer solstice, in Denmark it is also known as "Sankt Hans Aften" (St. John's Eve). People believed that at midsummer plants had miraculous and healing powers and they therefore picked them on this night. Bonfires were lit to protect against evil spirits which were believed to roam freely when the sun was turning southwards again. In later years, witches were also thought to be on their way to meetings with other evil powers.