The Backrooms

If you're not careful and noclip out of reality in the wrong areas, you'll end up in the Backrooms, where it's nothing but the stink of old moist carpet, the madness of mono-yellow, the endless background noise of fluorescent lights at maximum hum-buzz, and approximately six hundred million square miles of randomly segmented empty rooms to be trapped in. God save you if you hear something wandering around nearby, because it sure as hell has heard you.
In the Parallel Alice's Realm there is an anchored repeating portal from the Backrooms to that universe. The portal opens up precisely every 172 days 16 hours 23 minutes after the previous closing and 37.91 seconds and stays open for 5 hours 46 minutes 27.02 seconds.