The hardest 5x5 unit rush hour takes a still very impressive 199 moves and can be played at https://tromp.github.io/oriscript5.html https://tromp.github.io/oris

The hardest 5x5 unit rush hour takes a still very impressive 199 moves and can be played at https://tromp.github.io/oriscript5.html https://tromp.github.io/oriscript5.html That one is definitely humanly possible. The hardest 4x4 is only 40 moves as playable at https://tromp.github.io/oriscript4.html https://tromp.github.io/oriscript4.html All free to use.