I'm not really into 3-D, except to observe that 3-D tic-tac-toe, unlike 2-D, is a forced win for the first player.
Here's one you've probably already heard:
You are in a room with two doors. One door leads to freedom. The other door leads to a lion who will immediately eat you as soon as you open the door. You don't know which door is which. There are two guards in the room. One of them always tells the truth. The other always lies. You don't know which is which. You are allowed to ask one question of one of the guards. What question should you ask, so that you will know which door you should open?