How to make 1-way doors

1. Put some 1 way cubes (bugged cubes by pushing in the top corners) where you are going to put the door. Rotate them to the direction you want to enter the door.

2. Make the 1 way cubes invisible by selecting them and make their alpha values low valpha 0.001 0.001 and adding an alpha material. Note: Setting the alpha values to 0 will cause the cubes to be visible. (0 means disabling the alpha value)

3. Put the door in like normal and test. The door will still open if you go near the wrong side.

Note: If you don't want that. Just make the door solid and change the trigger value so it opens when a switch trigger is activated. Put the trigger in front of the door you want to exit and you can make the door close after a certain delay. Use the invisible 1 way cubes if you want nothing going the wrong way into the door.