After you take the elevater with headcrabs jumping from above, put the noclip cheat on, as well as the r_fullbright 1 cheat (to more easily find the isolated dark room). Go through the wall by the doorway and the metal barrels, look for pink cubic room below and enter it. All of the walls, ceiling, and floor is filled with Gabe Newell texture, co-founder of Valve. The room is actually used to spawn creatures before the player sees them.
By the door of the flooded kitchen in the office complex you'll find a board "Dr. Newell Chaos Theory R&D". This is a reference to Gabe Newell, co-founder of Valve.
