Try what inventor claims to be “the world's hardest simple sliding-block puzzle”. Here “simple” means that quzzle consists of three sorts of tiles—two one-by-one units, six one-by-two units, and one two-by-two unit. "Hardest" means to move the largest tile from one corner to another in minimal number of steps (which means 84).
I had fun today solving Jim Lewis' quzzle with minimum moves. It was hard. . .
Try it - when you finish, you will see this. Good luck!