Arkham Asylum is packed with hidden nods to the wider DC Universe:

- Scarecrow's Secret Room: In the Warden's office, use Explosive Gel on a specific wall to find a hidden room detailing Scarecrow's plans.
- Killer Croc's Cell: Visit his cell in the Intensive Treatment to hear a unique dialogue.
- Calendar Man's Cell: Find his cell in the Penitentiary; he's absent, but his calendar is marked.
- Arkham City Blueprint: A hidden blueprint for Arkham City can be found in the Warden's office, foreshadowing the sequel.
Keep an eye out for subtle references in character bios and environmental details.
Compare easter eggs & references inBatman: Arkham Origins