Arid Athenaeum

That area is completely different than that of the sewers. Its contents corrupt the mind, not the body. - The Caretaker when spoken to after dying there.

The Arid Athenaeum is the third area of the game. It's theme mainly surrounds that of a frigid library with monsters often featuring quick attacks and charging towards the player, with the difficulty of avoiding them augmented by slow bullet users and the uniquely slippery floors. It introduces the "falling icicle" trap that hangs on the ceiling, along with ceiling crawlers resembling the wall crawlers, implying they are its vertical counterpart.

The area also has a unique Mirror Room that is activated when you have Reflection.