Anamorphic illusions...

Anamorphic illusions...  These are illusions that only work perfectly if you're standing in a particular spot, with your head at a particular height.  These five are some of the best I've seen.  I especially liked the third one (click the little “Next” below right of each picture to get the next one).  The photographer did a nice job of showing you both the “sweet spot” for each illusion, and what it looks like when you're not in the sweet spot.

I've only seen two of these in real life: one in London, and the other in a stairwell of a business building in St. Louis, Missouri.  Both were good, but not as good as those in these photos.  The world needs more of these!