For years the residents tried to cross each bridge without repeating any of them. Many claimed theyd completed the walk in the middle of a drunken night, but couldnt repeat the feat in the light of day.
It was impossible to cross all the bridges without repeating any and laid the foundation for graph theory and modern topology.
Each level is designed as a graph, and unlike the real bridges all of these are solvable. For example, the level Tic Tac Toe graphs out like this: