1. The Golden Owl or 'La chouette d'or'
On the Trail of the Golden Owl (translated from French) is a treasure hunting book by Max Valentin (a pseudonym for Régis Hauser), whose final clue is yet to be solved. The book's artist, Michael Becker, drew the book's illustrations but also crafted the still-buried bronze owl and the museum-held golden owl—the prize for the one who solves the final clue. Unfortunately, since the book's publication in 1993, the owl's location has never been uncovered. The only one knowledgeable was Hauser himself and since his tragic death in April 2009, the golden owl has remained more mysterious than ever.
2. Lake Toplitz's 'Nazi Gold'
However, the unfortunate number of tree trunks lying at the bottom make it beyond risky for divers to search, especially alone. It's left many locals and outsiders wary to continue this scavenger hunt, even though Nazi relics (mostly munition and remainds of experiments) have been uncovered in past expeditions.
3. William 'Captain' Kidd's Treasure
However, Captain Kidd's treasure is still suppoedly out there, in a number of areas in the world. Treasure hunts take place in Nova Scotia, Connecticut, New York, New Jersey, and more. A forum entitled 'Unsolved Mysteries in the World' alo provides a fascinating, more in-depth account of Captain Kidd if you're interested.
4. Forest Fenn's Treasure
As no one's discovered the treasure, Fenn periodically release clues, including this riddle:
As I have gone alone in there
And with my treasures bold,
I can keep my secret where,
And hint of riches new and old.
Begin it where warm waters halt
And take it in the Canyon down,
Not far, but too far to walk,
Put in below the home of Brown.
Maybe you can solve it?