Cave in the Rhodope mountains, Bulgaria, carved by hand more than 3000 years ago (?), it was rediscovered in 2001. Archeologists hypothesize that an altar built at the end of the cave, which is about 22 m deep, represents either the cervix or the uterus. At midday, light seeps into the temple through an opening in the ceiling, projecting an image of a phallus on to the floor. When the sun is at the right angle, in late February or early March, the phallus grows longer and reaches the alter, symbolically fertilizing the womb before the sowing of the spring crops.

Stunning photo. Thanks to UrsaRodinia for this one.