According to Wikipedia, "Avebury is a Neolithic henge monument containing three stone circles, around the village of Avebury in Wiltshire, in southwest England. Unique amongst megalithic monuments, Avebury contains the largest stone circle in Europe, and is one of the best known prehistoric sites in Britain. It is both a tourist attraction and a place of religious importance to contemporary Pagans."
"Constructed around 2600 BCE,[1] during the Neolithic, or 'New Stone Age', the monument comprises a large henge (that is a bank and a ditch) with a large outer stone circle and two separate smaller stone circles situated inside the centre of the monument. Its original purpose is unknown, although archaeologists believe that it was most likely used for some form of ritual or ceremony."
And. What does the largest stone circle in Europe have to do with greyhounds? You ask.