When I was a substitute teacher I would give the kids logic puzzles of varying difficulty. I would offer $100 if anyone could provide me with the answer to this one. If they looked it up on Wikipedia and could then explain it to me, I’d give them a king size candy bar.

I never had to pay out.

https://en.wikipedia.org/wiki/The_Hardest_Logic_Puzzle_Ever

The Blue Whale is so large, that if you laid one out on a standard NBA basketball court, the game would be postponed.