Abstract: A puzzle is provided, according to the preferred embodiment, having a series of rectangular blocks assembled so as to be able to slide on the surface of a rectangular planar back panel mounted in a vertical orientation. A set of four frame members, two of which have engaging tongue members and two of which have engaging groove members, are attached thereto. Each of the rectangular blocks is configured with two perpendicular, adjacent edge tongue members and two perpendicular groove members oriented to mutually engage respective tongues and grooves of other blocks and of the frame members of the puzzle. One space substantially equal to the size of one block is left empty to permit block movement. Each block has a magnet adapted to releasably engage a complementary magnet on the back panel so that when the magnets are engaged, the block positioned above an empty block space will not fall into that space.