This strange secret level is accessed through a teleporter in Sector 1 after finding all 10 posters. Starta game and go to the upper left part of the level, but don't kill all guards on the way. There should be a lift with a breakable wall on the left. Usually there is a brown enemy Scout on the far right of the lift, but after collecting all 10 posters he will change into a grey Soldier (they have Rocket launcher attacks). You must lure the Soldier to the left and then dodge (duck) his incoming missle, allowing it to break the breakable wall to the left. Pass through the newly opened passage and enter teleporter to secret Sector Z. After accessing it once it is added to the Single Sector Warp list.