In 1982, author Byron Preiss released a book called The Secret. It contained 12 puzzles, each featuring a poem that had to be paired with a painting, which would lead to a treasure 'casque' containing a key buried in a park. Two had already been found.

In 2019, Jason Krupat believed he'd figured out that one was buried in Langone Park in Boston. He visited the park and was shocked to see construction work underway. "I got up the courage to walk onto the site and find the foreman, and I said, 'You’re going to think this is crazy, but I think there’s buried treasure in this park,'" Krupat told the Boston Globe.

His hunch was correct, and the discovery was filmed for TV show Expedition Unknown, which had highlighted the still-buried treasures in a previous episode. The 'casque' contained a key, which was later exchanged for a green gemstone called a peridot, valued at $1,000 (£712), in a ceremony in New York attended by Preiss's widow (he died in 2005).

Treasures found hidden in construction and building sites