"The object of Sokoban is to push all stones (or boxes) in a maze, such as the one to the right, to the designated goal areas. The player controls the man and the man can only push stones and only one at a time. The restriction of only being able to push the stones makes this game challenging: One can create unsolvable positions. Players will soon learn that this is the main obstacle in solving problems. Advanced players also try to find shorter and shorter solutions, measured in stone pushes and man moves." (http://www.cs.ualberta.ca/~games/Sokoban/)