A puzzle that challenges a person to set a knight on an empty chessboard, and make the piece move around (as it moves in a chess game), but to visit every square only once. The knight's tour is the most well known of a variety of "tours" and puzzles based on chess pieces. A "closed" tour (also known as a "re-entrant tour") ends on the same square on which it began and needs 64 moves. An "open" tour ends on a different square and needs only 63 moves.