Within Fort Sphinxmoth I encoutered one of the chapel guards. She believes more of her companions were still alive elsewhere in the complex
In the “Croc Pit”, there is an imperial who gives you a hint about the book by the door and the constellation panels that line the walls of the corridor leading to the door.
The panels are The Tower, The Lady, The Lord, The Mage, The Steed, The Thief
To unlock the door, click the panels in the following order
If you choose the wrong one, you will “zapped” but the panels will not reset.