Reminds me of Kit William's "Masquerade". I remember his coffee-table book that kicked off a treasure hunt in the '70's. I later read with fascination how the treasure hunt was planned, executed, and finally solved. The party that solved the puzzle did not in fact find the golden hare — instead an individual who had not solved it did.

https://www.goodreads.com/book/show/1176887.Quest_for_the_Go...

We need more hidden treasures, I think.