Sheela na gig

Attitudes towards proper church decorations have evolved over time.

Sheela na gig is the name given to carvings of naked women displaying an exaggerated vulva. Such carvings appear on many churches in Ireland and elsewhere in Western Europe (but mainly in Ireland).

From here with a fully version of the story. Wikipedia provides background on the phenomena itself.

The distribution corresponds more or less with Celtic Europe and before that with areas having strong Bell Beaker cultural influence. But the timing, in the Medieval Period, first appearing around the 11th century CE in Christian churches, complicates a straightforward connection between these images and Celtic or Bell Beaker pagan traditions. 

So too does the fact that they appear to have originated in France and Spain and began to appear in the British Isles only in the wake of the Norman Conquest (of 1066 CE) in areas that had been subjected to Norman rule, reaching Ireland, where they became most common, last of all in the 12th century, with "areas that remained 'native Irish' have few sheela na gigs" according to the source cited by the Wikipedia article.

The phenomena arises around Y1K, which is also around the time of the early Crusades, in which the Normans were prominent participants. 

It was a time of great Viking activity over vast distances. Harald Hardrada may have died in England trying to become king of that nation, but he served for a time in the Varangian Guards in Constantinople. His connections to Kievan Rus were such that priests in the Eastern Christian tradition were brought in to aid in the conversion of Norway, which was one of the last of the places to convert to Christianity made their conversion. In Norway, "the Urnes stave church, thought to be the oldest one still in existence" was built using timber from 1069 and 1070.