Mên-an-tol (for Pam).

Mên-an-tol; simply Cornish for holed stone.
A mysterious monument. The experts have no idea what this was for. All they know is that the allignment of the stones has been altered in fairly recent history. The stones were originally in a triangle formation, again no one knows why, nor why they were re-positioned at some point in the past 300 years.
More recently, babies have been passed through the hole for good luck and "...the ritual of crawling through the hole nine times widdershins was said to cure rickets and scrofula" - Craig Weatherhill in 'Belerion, Ancient Sites of Land's End'.