Found in the upper levels of the Giant Slave's cell in the Irithyll Dungeon. To reach it, the player must head through the toxic swamp of the Profaned Capital, up the chapel, and through a passage with a hole on the wall overlooking the giant and guarded by two invisible Jailers. The key lies at the end of the hallway.
Unlocks three cells in the Irithyll Dungeon:
- Unlocks a cell near the Irithyll Dungeon bonfire. Inside, a corpse holding a Rusted Gold Coin can be found.
- Unlocks both gates of a cell on the lower-east wing of the first cell block. Inside, a corpse holding the Prisoner Chief's Ashes can be found.
- Unlocks Karla's cell in the second cell block. The area is patrolled by several Jailers.