I was rereading Coraline, and I noticed something similar to Backroom Level 0:
"It opened on to a dark hallway. The bricks had gone, as if they'd never been there. There was a cold, musty smell coming through the open doorway: it smelled like something very old and
very slow."
"There was no brick wall on the other side of the door: only darkness. A cold wind blew through the passageway. Coraline made no move to walk through the door."
"Coraline took a deep breath and stepped into the darkness, where strange voices whispered and distant winds howled. She became certain that there was something in the dark behind her: something very old and very slow."
"She took her first step down the dark corridor. She could smell dust and damp and mustines."
"The candle cast huge, strange, flickering shadows along the wall. She heard something moving in the darkness, beside her, or to one side of her, she could not tell. It seemed as if it was keeping pace with her, whatever it was."
"Coraline turned her back on the door and began to run, as fast as was practical, through the dark corridor, dragging her hand along the wall to make sure she didn't bump into anything or get turned around in the darkness. It was an uphill run, and it seemed to her that it went on for a longer distance than anything could possibly go. The wall she was touching seemed warm and yielding now, and, she realised, it felt as if it was covered in a fine downy fur. It moved, as if it were taking a breath. She snatched her hand away from it. Winds howled in the dark. She was scared she would bump into something, and she put out her hand for the wall once more. This time what she touched felt hot and wet, as if she had put her hand in somebody's mouth, and she pulled it back with a small wail. Her eyes had adjusted to the dark."
"She knew that if she fell in that corridor she might never get up again. Whatever that corridor was older by far than the other mother. It was deep, and slow, and it knew that she was there..."
This was definitely not Backroom, but it definitely gives off them vibes.