Before you hit the streets of Arkham City, why not take a look at the lay of the land so you won't get lost while beating up bad guys? There's a hidden room to be found in Batman: Arkham Asylum that reveals concept art for Arkham City.
To find it, you need to head into Quincy Sharp's office: enter Arkham Mansion from the front entrance, head down to the second hall on the right, make a left, then reach the end to the office. On the left wall before the steps, plant three rounds of explosive gel and you're in. It's a super-secret area that doesn't count as any sort of achievement, archive, or Riddler clue so it's gone unnoticed for a good while.
What's to be found? There's an unmarked blueprint found on a desk while a nearby wall contains two pieces of concept art and a layout of Arkham City. While none of this may make it into the final game, players could be visiting a hotel, a steel mill, a psychiatric ward, and a penitentiary. And it's all just quick cross on a bridge from the Asylum.