I came accross this article about the theory of a retired professor of obstetrics and gynecology at the University of British Columbia. He believes the ancient site is a massive female fertility symbol. Here's an excerpt:
Viewed from above, Perks suggests Stonehenge's inner bluestone circle represents the labia minora and the giant outer sarsen stone circle is the labia majora. The altar stone is the clitoris and the open center is the birth canal.
"Could the outer avenue of Stonehenge...represent the way by which new life entered?" the article wondered, adding that when comparing "the layout of the henge with the anatomy of the human vulva. There is a distinct similarity."
I couldn't make up these things better. Maybe it was the site of the first Lilith Fair?