Old Conclave Vault
The Old Conclave Vault is a zone that is revealed by reading a note dropped by Director Hompalan in the Ruined Halfling Complex. Note that he will only appear if the Old Conclave Vault was chosen to spawn this game. In each game, only one out of Dogroth Caldera, the Sludgenest, the Old Conclave Vault, and (if Forbidden Cults is enabled) the Scourged Pits will appear. This is chosen randomly, unless you are a Shalore and have not yet unlocked Ogres, in which case this zone will always be chosen.
A few steps after entering you will be forced into dialogue with Ogres, and the only answer is fighting. After this you get four more levels of dungeon, but the thing here is that you'll see a bunch of impassible tiles which look like glass jars. Those will spawn various Ogre-themed monsters after you are in proximity to them for long enough. It's best to wait for them to spawn before moving on, or you'll get surrounded. There are also a fair number of traps on the floors.
The last level has Healer Astelrid, some sort of Ogre mage-priest who can hit pretty hard; but if you got this far and cleared all the other floors, you'll clear her out too. She drops a unique greatmaul which is pretty good for Ogres, less so for everyone else. Collect the lore she drops to unlock Ogres.