Batman: Arkham City was a pretty stellar and full-featured gaming experience, but the sentiment among many fans is that it would've been nice to explore the Batcave. Yes, Batman's lair is technically located beneath Wayne Manor, and yes, Arkham City's story doesn't unfold anywhere near the home of Bruce Wayne, but Arkham Asylum gave us a satellite Batcave to explore and it would've been cool to see one in City. Or WILL be cool, since the Batcave is now coming in DLC form.
The game's official Twitter feed confirmed that the Batcave DLC will be coming on December 20, along with the Joker's Carnival and Iceberg Lounge challenge maps that were previously available as pre-order bonuses. The tweet doesn't say anything about the DLC release beyond the release date, but it seems a safe bet that it'll take the form of a challenge map.