Would a Rubik's cube be a trapdoor function? It's easy to scramble a Rubik's cube but it is hard to solve, unless you know the algorithms for solving it. This makes it a trapdoor function, correct?
It might be a viable example for explaining the concept of a trapdoor function to a layman without a computer science or math background. But from a CS standpoint this is only half-true.

For a low number of n where n is the number of rotate-operations performed on the cube, it is true that finding a solution for the cube is more computationally expensive than applying the rotations. But with very high values of n this might change. It was proven that any rubic's cube configuration can be solved with 20 moves or less, and finding that 20 move sequence might in fact be faster than applying the "correct" sequence.