Batman: Arkham Aylum Guide
After you open the door and enter, you will see a new Riddler Challenge: “You don't know Jack about Gotham. Tune in to find out.”
Head down the stairs and along the hall to the end, turning left. About this time you pick up a radio broadcast of a news report in which the Joker features prominently – go ahead and stop and listen to this. When it is done, go through the door on the right (checkpoint) and tear open the grate, and follow this duct to the outside.
A path appears outside, so drop onto it and follow it for a cinematic mini-CS and the Achievement 'Born Free' (10GP).