What's The World's Hardest Puzzle?

Many puzzles, whether math problems, word challenges or physical objects like 3-D puzzles and scrambled cubes, involve staying at home, one-on-one, man versus puzzle, while others combine an object and a quest into the physical world outside the game. The Isis Adventure, often dubbed the world's hardest game, starts as players find a way to open a round puzzle they can hold in their hands. Once inside, a key leads them on a search for a real hidden prize. It is, after all called an "adventure," so removing the puzzle itself from the box is only the beginning.

What's the world's hardest puzzle?

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