Where the hunters go to get a cursed ring, and where ring-owners get found first.
Described by Mordecai as part of his case against the Night Wyrm's Ring. The sixth floor has hunters, and one of the main reasons they flock to the hunting grounds is to obtain a Divine Suffering artifact of their own. Every season, several such rings are generated, and every season the crawlers who own them are the first ones tracked down and killed there.
Mordecai's threat is specific: if Carl still has the ring when they reach the sixth floor, he will tell Princess Donut to stay away from him.
The sixth floor's crawler-hunting region, spoken of only in warning.