OK out, C to deselect. Click the top and bottom edges of S6, right click, go to "sidedefs." Click the top middle pane (front side middle texture), select DOORTRAK (or the wall moves when the door opens). OK out again and press S. Right click S6 and set ceiling height to 0. Press T, right click on the center of S3, then again, and select Keys - Red Skullkey. Do the same four times in S5, but select Weapons - Shotgun, Keys - Blue Keycard and two Monsters - Imps.