Around 1885, a short pamphlet was published in Lynchburg, Tennessee: it contained a story about a young man called Thomas Beale who had allegedly deposited a sizeable treasure (worth approx $63m in 2011) in two deposits in 1819 and 1821.
According to the pamphlet, Beale left behind three ciphertexts detailing where the treasure was buried and the names of the party of people who had discovered the treasure. However, only one of the three ciphertexts (the second one, known as “B2”) has been cracked to date, using a miscounted Declarationn of Independence: the location of its treasure, apart from a statement in B2 asserting that it was buried “four miles from Buford’s [Tavern]” in Virginia, remains unknown.
It remains an open question whether this story is entirely real, or partially real (e.g. that the ciphers are real but the pamphlet is fake), or completely fake.
A particularly interesting feature of B1 is that it produces sequences that are very far from random if you use broadly the same Declaration of Independence text as a dictionary for its dictionary code, which would seem to imply the presence of some kind of message there. However, this same nonrandom behaviour has also been cited (by the very well-respected historical codebreaker Jim Gillogly and others) as evidence that the text is meaningless. There’s some discussion on this apparent paradox here and here.
For the full text of the ciphers and Beale’s (alleged) letters, go to a dedicated Beale Papers transcription page elsewhere on this website.