This sculpture holds a decades-old C.I.A. mystery. And now, another clue.

New York Times:

The creator of one of the world’s most famous mysteries is giving obsessive fans a new clue.

Kryptos, a sculpture in a courtyard at the headquarters of the Central Intelligence Agency in Langley, Va., holds an encrypted message that has not fully yielded to attempts to crack it. It’s been nearly 30 years since its tall scroll of copper with thousands of punched-through letters was set in place.

Three of the four passages of the sculpture have been decrypted (the first, though unacknowledged at the time, was solved by a team from the National Security Agency). But after nearly three decades, one brief passage remains uncracked. And that has been a source of delight and consternation to thousands of people around the world.

I’ve been following this story as an interested observer (I’m nowhere near smart enough to attempt any solution) for years and I love the mystery of it.