You're thinking of the Kryptos sculpture, which is at CIA headquarters in Langley, Virginia (http://en.wikipedia.org/wiki/Kryptos http://en.wikipedia.org/wiki/K

You're thinking of the Kryptos sculpture, which is at CIA headquarters in Langley, Virginia (http://en.wikipedia.org/wiki/Kryptos http://en.wikipedia.org/wiki/Kryptos); "of the four messages, three have been solved"; it was installed in November 1990, so it's been almost 22 years.