Free The Key

A sliding block puzzle in a buried temple. The golden key is boxed in behind a wall of timber, and the only way out is a gap in the right-hand wall - so shift the blocks aside, one at a time, and drive it through.

Blocks slide along their own grain and nothing else: a block laid across moves left and right, a block stood on end moves up and down, nothing turns and nothing lifts over anything. Drag one and it stops dead at the first thing in its way, so clearing the path in the right order is the entire puzzle.

Forty-five doors, and not one of them was placed by hand. Every level was found by enumerating every position its blocks can reach and picking one at a measured distance from the exit - which means each is solvable by construction, and the move count on its tile is the true minimum rather than a guess.

The opening doors are four blocks and two moves; the last is thirteen blocks and forty-six. A hint, when you want one, is worked out on the spot by the same solver that proved the level, so it still helps on the twentieth move when you are nowhere near the intended line.

Undo costs nothing and restores the counter with it, three stars for matching the minimum, and progress is kept between visits.