Cracking the Code - The New York Times
I love this story. An architect enlists his friends to help create a mysterious scavenger hunt within his clients' home. For free. He didn't even tell them about it and they didn't find the first clues until after they'd been living there for over a year. Then at one point they got a poem in the mail that gave a clue of where to find a book that had been written entirely about a false mythology of the house and historical figures.
It's a beautiful project. And it's awesome that the family living there gave him enough license to do what he wanted to do, that he was able to do all of this without their knowing.