Open the door in front of you, and run down the stairway to the northwest. Dash to the blue key in the west, and return to the nexus. Open the blue door, and head to the passage in the southeast. Head north through the passage, climb onto the walkway, and open the door. Go onto the southeast walkway, and travel on to the teleport pad in the northeast. Step onto that teleporter, followed by the next one. Grab the red key, drop down, and return to the courtyard. Open the red door in the northwest, and flip the switch.
Other points of interest
At the start of the level, open the demonic face to the east to find some shells and a backpack. (sector 84)