Algorithms for making more interesting mazes
Another interesting aspect of the grid coloring approach is that one can pre-bake larger rooms within a maze, which is useful when adding a maze to a different style game, such as a first-person shooter or an RPG.  Other features, which aren't provided by the standard Prim's Algorithm, such as 2.5D mazes (bridges and tunnels), or having more than one path to a given room, can be added after maze generation has been completed.  A bridge, for instance, can be added by connecting two locations and adding a wall to block off one of the locations from the algorithmically defined path, if maze continuity is desired.<p>I played with using mazes as a way to find things that are quickly solved by machines but take some concentration from users, as a sort of anti-CAPTCHA test.  Obviously, there are thousands of such potential tests, but mazes have an aesthetic appeal lacking, in say, "find the prime factors of this 128 bit number."  A child can brute force a maze, as can any adult, given enough time.  A machine breezes right through large mazes that could take hours for a human to solve by hand.  When would such a test be useful?  I'll leave that to the imagination of the reader.