All over Ireland and Great Britain are found enigmatic carvings of female figures displaying prominent genitals. Usually the figures are hunched, squatted, or crouched down, stretching their labia with their hands in a gesture that reminds one of the Internet's "goatse" meme (just with a different orifice).
Oddly for its brutally grotesque and exhibitionist attitude, the figure's motif is often found in church architecture, as well as decorating castles and other historic buildings. The mysterious part is that nobody can say for sure why, or how it incorporated itself into European architecture. It appears in history starting about in the 12th century. It is found in France, Spain, Scandinavian and Slavic countries.
Scholars heatedly debate the lineage of the figure. It is variously said to be Pagan, Wiccan, Celtic, or even related to South Seas fertility symbols. This historian makes a strong case for linking Sheela Na Gig with the mythical crone archetype. Meanwhile, fan pages are all over the web, such as this Tripod site devoted to Sheela Na Gig (Tripod sites themselves being a historical anomaly).
But the grandma of all Sheela Na Gig sites is sheelanagig.org, a vast resource dedicated to tracking down and exploring every corner of this strange mythos. Is it a fertility figure, a deity, an erotic symbol, a gargoyle, a demon, or a reminder of both birth and death? Perhaps, like all mind-blowing art, it is all of these, open to whatever meaning the viewer wants to project.