Go back to level 10 where the map of the maze spells out "KEY". Move through the maze to the point in the middle of the top of the Y ie. |_ _ _ |(middle). Then move one square left and look at the wall when you face north. There will be a switch that opens the bottom of the Y. At the bottom of the Y will be a code. Write it down as it changes each time you go into level 10. The code represents the amounts of clicks on each of the level 20 buttons. Click the button after entering the code to reveal the door. To get the key, go to the keypad and click slightly right of the keypad to make it turn and you can view the right hand side of the pad where the key is.