This level occupies the map slot MAP04. For other maps which occupy this slot, see Category:MAP04.
From the map start, descend the stairs into the yard. Go through the western hallway, descend the curved stairs and push the switch in the east with a bulk cell in front of it to lower the part of the walkway where the rocket launcher and nine rocket boxes are located. Some (two on easy, four on medium and six on hard skill levels) revenants will teleport in the lowering part of the hallway. After wasting them, ascend the curved stairs again and run through the hallway, jumping over the new gap. On the eastern side, step close to the southern wall next to the gap and look to the northwest. You should see a shell box, a backpack and blue armor ahead. Simply run forward to jump on the ledge (sector 59) to collect those items. You can come back to here later in case you don't need all items by now.