In the game, fairly early in the story (The part where Batman chases after Harley Quinn the old fashioned way by climbing up the elevator) There is a vent underneath the elevator. Go to the right, you'll see the connecting vent. If you go through the vent you can see all the way through, and go underneath the crushed elevator. BUT there is ANOTHER way, and it leads to one of the many hidden rooms in the asylum. Lined with human skulls, and millions of pictures of Batman like someone was stalking him. And more pictures of creepy face, and quite a few blueprints, and to add to that....a computer with security footage. Also in the room, there is some mushrooms that grow in the corner. If you want more information about this secret room, be free to comment any question, feel free to ask!