I don't know if anyone's interest here in words extends to cryptography or not, and furthermore this is old news (more than 10 years), but there is an interesting sculpture at the CIA headquarters in Langley, VA that features a lengthy encoded message. (Its four parts have apparently been decoded already by skilled amateurs.) See http://www.elonka.com/kryptos/KryptosAerial.html and http://www.elonka.com/kryptos/KryptosAerial.html. (You can also search Google for Krytpos and find lots of stuff.)

For a code/cipher challenge that does not require a Ph D in applied mathematics, check out http://www.cryptex.org/hidden.html.