Dead Cells

You gain access to the Slumbering Sanctuary after beating conjunctivitus in the Insufferable Crypt. When you beat them, you can progress through to the door which is "Slumbering Sanctuary".

Prisoners Quarters -> Toxic Sewers -> Ancient Sewers -> Insufferable Crypt -> Slumbering Sanctuary.

I've linked a video below as well as a full playlist showing you how to get all areas/runes.


Full playlist:
https://www.youtube.com/playlist?list=PL2QolhM4SgygXMJl5CQ6Z...