Archaeological site Mên-an-Tol in Cornwall

You're standing at Mên-an-Tol, out in the hills of west Cornwall, about three miles northwest of the village of Madron. Look at the three granite stones in front of you. On either side stands an upright stone, each around four feet tall. Between them is the famous one: a round, roughly eight-sided stone with a hole half a metre across. Just big enough to crawl through.