Chess enthusiasts, and those who carefully read the FIDE Laws, would have noticed we played a little trick. Each player always begins with a white square in their near right corner. Therefore, we are viewing the above board from one of the two sidelines. It isn't readily apparent which sideline, but as it happens it doesn't matter. Assuming white knows what side she started from, she can promote the appropriate white pawn to a queen. And either way, she guarantees a mate.

Incidentally, the game would be a draw if white ended her turn with Black un-checkmated, but with no legal moves.

This puzzle is based on one posed by Erwin Brecher in "Puzzles, Mathematical Diversions, and Brainteasers".