Hell Gate (Maugrim Woods)
Faction title: The Gate of the Dead
Faction map name: The Gate and the River
Start room: The Gate Room
Finish room: Hall of Judgement
Faction info: On the other side of the gate once guarded by Kerberos, the Judge of the Dead awaits any would who come his way.
Added: 30th April 2021
GoWDB link: Hell Gate - Kingdoms - Gems of War Database
Faction weapon (Hellblade): Hellblade - Weapons - Gems of War Database
Faction pet (Slightly Judgy): http://gowdb.com/pets/13160
1 room is a firm treasure, 6 others are occasional treasures. But my estimation is about 2 treasure rooms per delve. Sometimes you’ll see only 1 treasure, sometimes - 4 (I never saw 6 or 7, can’t guess what are chances of this event). The most rare treasure room is IV, I saw it as an actual treasure only in 1 of 60+ delves.