Callanish Stones, Isle of Lewis, Outer Hebrides, Scotland, 2009.

Callanish Stones, Isle of Lewis, Outer Hebrides, Scotland, 2009. The Neolithic stone circle at Callanish (Calanais) dates from approximately 2000 BC. It consists of a ring of 13 stones of Lewisian gneiss, the tallest of which marks the entrance to a burial cairn, although archaeologists believe the cairn was a later addition to the site. Various theories exist concerning the purpose of the circle and the nearby other rows and avenues of stones, including the possibility that they functioned as a form of lunar calendar. A local legend says that the stones are 13 giants who were turned to stone by St Kieran when they refused to convert to Christianity. (Photo by Peter Thompson/Heritage Images/Getty Images)