The dungeon's sixth floor — the one place outsiders can truly die, where level-30 'hunters' grind gear to sell to the ninth-floor factions.
The Hunting Grounds are the dungeon's sixth floor, explained by Mordecai as Carl probes for a plan. Unlike the protected ninth-floor Faction Wars, the Hunting Grounds are the only place where outsiders can genuinely die. 'Hunters' — outsider tourists not tied to any faction, plus faction members after gear — start at level 30, may begin arriving once the crawlers hit the third floor, and can sign up until the sixth floor opens, grinding the appropriate mob areas (lethality only switches on when the crawlers arrive) to win gear they sell to the factions around Larracos.
By the time crawlers reach it, hunters are often around level 50, though the season's shortened timers likely mean lower. Carl's pointed questions — who can join, and by when — mark the Hunting Grounds as central to whatever audacious scheme he's forming.
The sixth dungeon floor; mob-hunting grounds and forests where outsider hunters level up (not described in scenic detail here).
The lethal sixth floor where outsider hunters grind gear — and the linchpin of Carl's forming plan.
Also appears in books you've already read — spoiler-safe to their endings: