Level 23.1 is a sub-level to Level 23, part of Ending 1 to level 23. Upon entering the room it appears to be an empty waiting area, devoid of any furniture but a few windows and doors leading into locked rooms. Continuing to walk throughout the level will bring you to another place that looks like a break room, or office area to a hospital. Further exploration leads into a room full of panels separating stretchers and UV's. There is a vent above one of the stretchers. Once entering the vent you need to crawl to the other side to complete the puzzle inside said ventilation. There is also a scene here in the first vent dropdown shaft where you can see the watcher teleporting the Titan Smiler here, and then pointing it in a direction in needs to go.

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Objective

Within the vents are rectangular shapes that are able to be turned. Each side has a different color, green, blue, yellow and red. There is in total 3 of them, and there is numbers next to them to indicating what order they are in. Once you exit the vent there will be buttons lighting up in a certain pattern showing you what order you must flip the lights to. Once you do this the exit gate will open up. It leads to a dark hallway, with a little someone you saw earlier.

Once you enter the hallway and get close enough to the darkness the Titan Smiler you saw earlier will emerge from it, it will then begin to chase you. The entire sub-levels lights will then begin to turn fully red. You must go back into the vent and crawl through it. The gate that was closed when you first entered the vent will open up leading to a new place. Upon exiting the vent the chase will stop and the Titan Smiler will be unable to reach you. You will now have to continue walking through the sub-level until the Watcher appears again to tell you what to do.

The exit to the sub-level is a hole leading into a mono-yellow colored void. Possibly a reference to the backrooms google earth/maps incident.