Jim Sanborn created a sculpture containing a secret message. It sits on the grounds of CIA headquarters in Langley, Virginia. Yet no one has been able to solve it.

Code breakers from around the world have tried for 30 years. They’re stumped. The artist meets with people like cryptologist Elonka Dunin who are desperate to solve the mystery at his Maryland studio every year or so. But Sanborn won’t divulge any clues. It’s too much fun keeping everyone guessing.