An 1885 pamphlet claimed a fortune in gold lies buried in Virginia, its location locked in unsolved ciphers. Skeptics say the treasure never existed - yet people are still digging.

In 1897, Edward Elgar slipped a young friend a card covered in 87 curling symbols. She never managed to read it, no one has since — and the man who wrote it took the answer to his grave.

In January 2012 an anonymous image on 4chan promised to find "highly intelligent individuals." Three global puzzle hunts later, a runic book remains unread — and nobody knows who was asking.

For over 250 years, a short row of letters carved on an English garden monument has defied every attempt at decipherment - reportedly including Darwin and Dickens, and certainly the codebreakers of Bletchley Park. Eight letters may be too few ever to prove any answer right.