# Anyone know of an impossible, trick puzzle? [closed]

My dad really likes mechanical puzzles and has drawers full of them to show to people. My family has decided that it would be a great joke to find a new one that he hasn't seen, that is actually impossible to solve. Of course we wouldn't tell him that though. Does anyone know of any puzzles that fit that bill?

The SE math stack has one here. It is known as the "Figure Eight Puzzle" and is a "disentanglement" puzzle.

• That sounds great! I wonder if anywhere actually still sells this, or if I'll need to make my own. Commented Jan 6, 2019 at 20:39
• Isn't "SE math stack" redundant? Commented Jan 7, 2019 at 23:52
• @PeregrineRook it could quite possibly maybe be so. Commented Jan 8, 2019 at 0:40

It might be too well known, but Sam Lloyd's 15 puzzle is famously known to be impossible:

Slide the numbers within the frame to get the numbers in order (ie swap the 14 and 15) $$\begin{array}{rrrr} 1 & 2 & 3 & 4 \\ 5 & 6 & 7 & 8 \\ 9 & 10 & 11 & 12 \\ 13 & 15 & 14 & \end{array}$$

Another famous one, which you might be able to make easily with cardboard or wood if you're handy, is to place thirty-one 2x1 domino tiles onto a chess board with two diagonally opposite squares removed. Each domino covers two adjacent squares.

• Came here to mention the 15-puzzle one. It also generalizes to be unsolvable for any board configuration that's an odd number of swaps away from the solved state.
– user33097
Commented Jan 7, 2019 at 19:23

I've read a book which featured just this kind of a puzzle recently.

In Red Sister/Gray Sister (don't recall which volume it was) by Mark Lawrence, there is a test which involves getting to a place without being noticed, finding a puzzle box there and opening it (which had a bunch of puzzle locks on it - this part of the description is vague). Nobody has ever succeeded on the last step, because the box was not actually a box, but a solid block of wood with the locks serving as red herring.

I don't know whether any such puzzle are for sale though.