In the mid-90's I pondered the Kryptos sculpture through a window of a CIA dining facility and was intrigued enough to wander out into the courtyard to take a closer look. Being the Marine that I am, I thought okay, some NSA bubba will solve this, now back to real business - and up to now I thought the riddle had been solved. Apparently not, at least according to John Schwartz at The New York Times.
And from CIA's HQ Tour site:
"Unbreakable codes. International intrigue. Even the CIA's artwork has secrets. Kryptos, a sculpture at Agency headquarters, has baffled code crackers around the world with its secret message. The copperplate and granite sculpture symbolizes both the history of cryptography and the significance of intelligence gathering. Mystery continues to surround this work of art -- no one has ever fully deciphered Kryptos' coded message."