Behold: Kryptos. A Linguistic Lock with 870+ Tumblers.

http://en.wikipedia.org/wiki/Kryptos

This is just fascinating.  Imagine the work Sanborn put into designing this.

A quote from Wikipedia: 

"Kryptos is a sculpture by American artist Jim Sanborn located on the grounds of the Central Intelligence Agency (CIA) in Langley, Virginia. Since its dedication on November 3, 1990, there has been much speculation about the meaning of the encrypted messages it bears. Of the four sections, three have been solved, with the fourth remaining one of the most famous unsolved codes in the world. The sculpture continues to provide a diversion for some employees of the CIA and other cryptanalysts attempting to decrypt the messages."


You can visit the CIA website about Kryptos HERE:
https://www.cia.gov/about-cia/virtual-tour/kryptos/index.html