Slide blocks in a 4x5 box, no lifting allowed, to free the big one
The classic Klotski puzzle packs differently sized rectangular blocks into a 4x5 box, including one large target block near the top. Moving pieces only horizontally or vertically within the box, and never lifting or stacking them, how do you free the target block through the exit at the bottom, in as few moves as possible?
Reveal the answer
The standard layout (one 2x2 block, four 1x2 blocks, four 1x1 blocks) is commonly solved in a minimum of 81 moves, found by shuffling the small pieces aside to open a channel for the big block to descend. The name comes from the Polish word for 'wooden blocks' (klocki), though the puzzle's exact origin is undocumented; it only became globally known after a 1991 Windows computer version popularized it.