The sleeping place of Scolopendra, third of the three realms the broken Nothing drains into.
When The Nothing broke, the third of the three system messages announced that it was currently draining into Scolopendra's Lair. One message later, Scolopendra stirred; a handful of messages after that, she awakened.
Her lair is described in terms of layers, and the only place the system named as safe from her impending attacks is the sixteenth floor, Agony Mirrors, precisely because it sits outside those layers.
The place where the draining Nothing wakes the dungeon's sleeping horror.