Puzzlers, enigmatologists, and even professional cryptologists have yet to solve “K4,” the fourth and final encrypted puzzle on a sculpture on the grounds of the Central Intelligence Agency’s headquarters in Langley, Virginia.

The 10-foot-tall plate, one part of the “Kryptos” artwork created by artist James Sanborn, now sits in the courtyard of the New Headquarters Building at the George Bush Center for Intelligence. It serves to inspire, not just by evoking emotions and encouraging self-reflection, but literally by encouraging those who view it to uncover its hidden message.

Installed in 1990, Kryptos was meant to challenge employees to break four encrypted messages.

As explained by the Associated Press, the “S-shaped copper screen” was meant to resemble “a piece of paper coming out of a fax machine,” while the CIA actually suggested it “looks like a piece of paper coming out of a computer printer.”

The sculpture contains four enigmatic messages, which the CIA explained were “each written in a different code,” described as being “important to the history of cryptography.”

The purpose wasn’t just to educate, but to entertain. Sanborn told the AP that he wanted to create something fun for those who worked at the CIA and regularly saw the piece.

“At the time, codes and encoding was an esoteric subject,” Sanborn said. “I wanted it to be less so, and I wanted it to be fun. … Any artist’s goal when they make an artwork is to have the viewer’s attention for as long as possible.”

Sanborn worked for four months with a retired CIA cryptographer to ensure that the first three encrypted messages, known as K1, K2, and K3, would be quickly broken. They were easy, relatively speaking.

The CIA acknowledged in 1998 that it had cracked the codes for three sections. The solution to K1 and K2 involved using a

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