Locked exit
Keys sit in dead ends when the maze has enough of them. Diamonds mark each key. Standing on the exit early does nothing until the last diamond is gone.
The board is still a perfect maze — one route between rooms. Keys only change the goal: visit every diamond, then the coral gate opens. Expert is twenty rooms with three keys; smaller sizes plant fewer diamonds.
Walking habit
Clear a stub when you pass it. Coming back across a large board for one missed key is how times blow up. Hint and Peek still work; both spoil Marks for that run.
Walk with keys Expert 20×20 Right-hand after the diamonds
FAQ
Why won’t the exit open?
You still need a key. Check the diamond count in the status line.
Do keys add loops?
No. Fog and keys never add loops. The exit stays on the same spanning tree.