If you think you understand 3D Tic-tac-toe pretty well, try taking it to another level - four dimensions. This one is somewhat hard to visualise - the easiest way to do this is to picture 3 sets of 3d Tic-tac-toe playing boards side by side, with the choice of set representing the forth dimension. It's quite a challange to play, and is a good tool when discussing four dimensional geometry with someone.

Because of the amount of effort involved in drawing up the playing field, we usually play until someone has a row of three and then black out the used positions and play in the remaining space only. As the board fills up it become harder to find a plane in which to attempt to create a line, increasing the difficulty level further. This method of play also eliminates the problem of the person going first being able to win every time - Since the 3D playing board is a subset of the 4D board tactics this tactic will also work in this game, provided there is a 3 dimensional block of 3x3x3 positions available.