Let's play with optical illusions... I think this one is amazing...

Albert Einstein Marilyn Monroe Illusion When you look at this picture close range you see Albert Einstein. Now stand up and take several steps back, roughly 15 feet away, It will become Marilyn Monroe.

and there was another one...

Graffiti Stairs Illusion In this subway, this guy spray painted the wall to appear as an illusion of the stairs coming out of the wall.

hmm.. isn't this challenging?