Go to the South city water area and into the left corner (there should be a small square building with a door). Jump on the roof, orient your camera facing back towards the center of the water area, then roll off just above the door. If you do it right, you will hit the ground, the door will open briefly, and you should be able to get inside. Once inside, you can use R3 to look around, or press up on the camera repeatedly and you will suddenly be in an elevator. At the bottom of the elevator is a cool platform with blue stretching in all directions. You can kinda see the block puzzle in the upper left corner. When you die there you will reappear next to the Titan suit in the underport. This glitch cannot be accessed until you get to "Rescue Sig in the Underport".