Officially christened the Noodle by Donut, and proven to have its own gravity: down is simply toward the nearest interior wall.
When Elle McGib asks on the chat what everybody is calling the in-between space, Princess Donut answers in capitals — WE ARE CALLING IT THE NOODLE — and the name sticks.
Elle then works out how it behaves. From Station 12 the hole goes all the way through to the room on the other side, a twenty-foot drop, with another door visible; that far room is also burnt out, and upside down. The rock she drops against instructions falls into the far room, falls back, clips the lip of the hole, bounces once, and rolls along the interior of the tube. Down, therefore, is toward the closest interior wall — you could walk a loop-de-loop inside and feel upright the whole way, like a carnival ride that spins fast. She wonders what would happen to a rock balanced exactly in the middle.
No Krakaren have come through the noodle for a while, but the Province Boss population has begun seeping through it into the opposite rooms, occupying both ends at once, so that crawlers returning to an abandoned station 36 find a boss waiting. Prepotente and Miriam Dom are on the far side of Carl's own stretch of it, close enough to talk through the hole.
A hollow tube layer between the floor's two mirrored storeys, twenty feet deep, its interior surface acting as the floor from any angle.
The hidden layer the swarm lives in, and now a two-way conversation pipe between rival crawler teams.