Ruy Lopez Exchange Puzzle (Rated 1069): Win a Queen — Ruy Lopez
Winning the enemy queen is the biggest swing available in a middlegame. When a player's last move leaves their queen undefended while attention is fixed on an attack elsewhere, the defender strikes: a bishop already looking down the diagonal to the queen's square captures it on the spot. The capture refutes the whole plan, since no counterattack outweighs the loss. Any desperate kingside counterplay is met by a simple recapture, and Black walks away with a decisive material advantage.