Opens up a shortcut from the Lamp, into the building, and unlocks a path to the Lumenflower Gardens.
- The area it unlocks is entirely optional, as is all of the Upper Cathedral Ward.
- Instead of going down and around the whole building to kill the Brainsucker that holds the key, players can use the Beast Cutter's transformed state's backstep strong attack to aggro it and make it get close to the door. When it is close to the door, players can just attack it and kill it from the other side.
- The key seems weathered from being poorly kept. Makes sense as it is being held by a Brainsucker who likely never realised it had it to begin with.