Former door of Carrizo monastery, Spain.
Notice how the pattern isn’t symmetrical on both sides. This was done to create a maze. Many cultures use this technique in various ways to protect something against evil since evil spirits will lose their way inside the maze but the good ones will get through.
(As I am from Canada I would like to add that the same concept applies to the Natives Dream Catchers)
by Monestirs Puntcat on Flickr.