Assassin's Creed Origins: 10 Things It Needs To Deliver
7. The Underworld
Egyptian religion was complicated, but long story short, the land of dead, or Duat (namechecked by Bayek during the demo mission), is ruled by the god Osiris.
The sun god Ra drove his chariot through it every night, and it was divided into twelve regions to represent the hours of the night. Guidebooks explained how the deceased could make their way across Duat to the place where they were judged and either eaten by Ammit, Devourer of Souls, or passed on to the good bit of the underworld where they could party with Ra every night.
That's all pretty badass, if a little too God of War for an Assassin's Creed game. But taking a cue from the Followers of Romulus from Assassin's Creed: Brotherhood and their underground lairs, Duat could be reflected in a physical underground location inhabited by cultists and madmen for Bayek to explore.
A religious sect that builds a 'real' version of the underworld is about as Assassin's Creed as it gets, especially when Bayek starts introducing them to the real thing.