The prize is as unique as the hunt itself. It’s a golden casket that was given to France by England before the signing of a diplomatic agreement in 1904. The casket was made by Goldsmiths and Silversmiths Company in London, and contains a scroll celebrating the two countries’ friendship. It’s valued at $892,000.

Vincenzo Bianca, who created the books’ puzzles, told The Guardian, “It was Michel Becker’s idea. He found the golden case, bought it, and learned everything that you can know about the Entente Cordiale [Anglo-French diplomatic agreement]. He fell in love with this story between France and England, which existed thanks to the will of the two men [King Edward VII and Loubet]. He wanted to bring this story to the world with this treasure hunt.”

Bianca and Becker wrote in the book, “A paper and a pencil will be enough to discover some solutions. For others, you will need to do additional research … the internet will be a valuable ally in finding the information you need without leaving your chair. This is not an easy treasure hunt. In order to conquer it, you will need tenacity: a treasure is accessible only to the brave.”