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.

Kryptos is a sculpture by American artist Jim Sanborn located on the land of the Central Intelligence Agency (CIA) in Langley, Virginia. Since his ordination on November 3, 1990, there has been much speculation about the meaning of the four encrypted messages that he bears. Of these four messages, the first three messages have been resolved, while the fourth message remains one of the most unsolved codes in the world. The statue continues to appeal to cryptanalysts, both amateurs and professionals, who are trying to decipher the fourth part. The artist so far has provided three instructions for this section.