The interiors of fortresses set to guard Avernus are not so complicated as mortal fortresses, they need not food nor places to sleep, only mazes of traps to also serve as garrison.
Behind the inner gate is the entrance to dull metal hallway that branches out left and right from the gate's opening. And a next sentry there, a nightmare of chains linking bladed cogs and jagged gears; a Castigas, a thing stupider than the Osyluth but more dangerous did it choose to fight.
Dozens of pitted lenses take in Aspexia Rugatonn, and then the mass of chains clunks forwards into the left-hand side of the maze, assuming (Carissa's bracer will tell her) the submissive posture of a guide who walks ahead of its superiors.