The Orphanage is another hidden location in the game which requires the Orphanage Key item.
After opening the large door at the upper cathedral ward, you may either return to the hunter’s Dream first and stock up on items or spend your Blood Echoes since this will be a boss fight.
After the large door, turn left and climb the stairs that will lead you to a bridge. There will be a Celestial Being waiting here for you to defeat. After defeating it, you may proceed and walk on to a large room where more Celestial Beings appear. If you move on towards the room, you will battle the Celestial Emessary.
There may be a lot of Celestial Beings appearing, all you have to do is keep on attacking the enemies and wait for one of them to grow – that is the Celestial Emessary. After defeating the Celestial Emessary, it will reward you with Communion.
After defeating the Celestial Emissary, you may smash the window in-front of the newly-lit lantern where you will find yourself in a hallway. From a nearby corpse you may pick up “A Call Beyond”. Going forward will bring you to an elevator. Taking that elevator will bring you to the Altar of Despair where you will find Ebrietas, Daughter of the Cosmos—a non-aggressive beast.
But if you do attack it, hitting it at the head seems to be the most effective way to deliver some real damage. Ebrietas hits real hard so it would be best to attack her at her back. Just like most of the enemies here, things change when you are able to put their HP down to 50%--for Ebrietas, a magical shield will be charged around her. Also make use of the time delay available whenever she smashes the floor.
When all your hits have landed and all your dodges prove successful, you will be rewarded with the Great Isz Chalice after defeating Ebrietas.
You may check out the Altar right beside where you found Ebrietas. If you attacked Queen Annalise at Cainhurst, you may resurrect her at this altar.