Kryptos

A copper scroll of a sculpture standing in the courtyard at CIA headquarters in Langley, dedicated on 3 November 1990, with four encrypted passages punched through it by the artist Jim Sanborn. Three are solved: K1 and K2 by Vigenere with the keywords PALIMPSEST and ABSCISSA, K3 by transposition, and the plaintext carries deliberate misspellings, so the first passage reads IQLUSION rather than illusion, on purpose. K4 has held out since 1990 and is one of the most famous unsolved ciphers in the world, with 97 characters and nothing but the clues Sanborn has let go of himself: in 2010 that NYPVTT is BERLIN, in 2014 that MZFPK is CLOCK, which points at the Berlin World Clock, and in 2020 that QQPRNGKSS is NORTHEAST and FLRV is EAST. In August 2025 he announced he would auction the solution, and the archive sold that November for 962,500 dollars, so somebody now owns the answer.