One game. Two worlds.
Classic chess, with an Underground beneath the Surface. Both boards share the same squares; every piece starts above.
VIEW RULES
Underground Chess Rules
Just the essentials. The best surprises are waiting on the board!
Now you see it… now you don’t!
Tunnel to the matching square on the other layer, even to capture an enemy there. One layer switch can change everything.
The knight’s secret shortcut
Knights can also jump in an L to an empty square on the other layer for free. L-shaped captures stay on one layer.
Every tunnel counts
Normal tunnel uses depend on surviving pawns.
Don’t use normal tunnels on consecutive turns of your own: Freeze blocks the second.
Out of tunnels? Not so fast!
You can recharge an empty quota: move your king onto the enemy king’s starting square (e8/e1) on the same layer, or move another piece onto e1/e8 opposite an enemy on the other layer.
A check from another world
A piece can check a king on the matching square below or above. A legal check-giving tunnel costs no normal quota. Your king must stay safe!
The king’s escape route
When checked, your king has up to eight special tunnels to safe squares.
Paired piece losses or spending the last normal king tunnel before the ONLY phase reduce that reserve.
Where the kings meet
When either side has 0–1 check escapes left or only its king, both kings sharing a layer bring the game to that layer — ONLY MAIN on the Surface or ONLY TUNNEL Underground. Moving toward that layer ignores quota and Freeze. If the kings are apart, KINGS ONLY lets either king safely join the other; a checked king may still safely capture the exact checker on its mirrored square.
How does it end?
Checkmate wins! Stalemate, repetition, the 50/75-move rule or agreement can end in a draw.
Clocks and takebacks depend on the game mode.
The rules are only the beginning. Where will your first tunnel take you?
Play and discover →