This quest involves collecting a series of keys which will unlock the way to the Oversized Banderling Ogre and his Platemail Hauberk. This quest can also be completed with lockpick skill (max. door resistance is 142).
Head back into the room with the benches and unlock the door (res.100) to the north with your key.
Go up the stairs to a small room overlooking an area with two Lichs and a Banderling Bloodblade locked inside a room directly beneath you.
Jump down whilst taking care as the Lichs cast spells that could kill a lower level character.
Dispatch the Lichs and unlock the door (res.100) to the Bloodblade, kill it and loot the Rusty Key
Antique Key
Exit this area through the south door and go left heading east into the prison cells section of the dungeon.
Continue on and turn right just before the lone Banderling Ogre that is guarding a chest.
The second cell to your right has a strangely Large Silver Rat. Unlock the doors (res.82) with the rusty key and kill it for the Antique Key.
The Platemail Hauberk
Return to the Banderling that you saw before and head south down the corridor behind it.
Unlock the doors here (res.142) with the antique key and take the stairs down until you reach the caverns.
At the split hug the right wall heading southeast before heading up some more stairs to an open room with some Banderling Blades and a Drudge Servant.
From here, take the east exit following it down a very long corridor. Once you meet some rooms at the end, go north and then west into the room with the Oversized Banderling Ogre.
The dungeon also holds the Alloy Tool used for the Undead Mechanic Quest.It can be found by taking the east passage from Granite Golem/Prison portal area.
This quest became part of the Facility Hub during the Reforging the Past event and received many changes including updates to the creatures that drop the keys.
