Batman: Arkham Asylum Guide - Walkthrough
Ahead of you is a Zip point above that you can reach after you jump the small partition – go ahead and zip up there so you can listen to the Joker's security alert and take a look around at the same time. Below you is a cage with a Trophy in it – that you cannot reach from here – and you should notice if you pop on Detective Mode that there is a grate behind it in the cage as well. Below you there is a grate you can reach, so after Big J finishes drop down and hit that grate.
As you follow the duct you will notice that your path can split at one point – either going forward or turning to the right. Take a brief detour to the right, following that duct down to the aforementioned grate, and grab the Trophy for an easy Achievement: 'Arkham Analyst' (20GP).
Now backtrack and continue on to the right – and shortly you will drop down a shaft that gives you access to the room full of enemies. There are Gargoyles ringing the room – so go ahead and zip up to the nearest one, and then zip across to the Gargoyle above the end of the catwalk where the two enemy are patrolling.
Here is a chance for you to pick up a nice Achievement if you want – assuming that like me you went ahead and grabbed the Inverted Takedown upgrade... Hit B to hang from the Gargoyle and when an enemy walks near enough, hit Y to do the Inverted Takedown, leaving him dangling from the Gargoyle. Now zip to a nearby Gargoyle and switch to your Batarang, then wait for another enemy to walk beneath the dangling one while you are targeting the rope he is dangling from.
When the enemy is below him, hit the rope with your Batarang, severing it and dropping him on the hapless enemy below for an easy 10 GP and the Achievement: 'Rope-A-Dope-A-Dope'!
Now pick off the remaining goons as you like – a few more hanging goons might be fun. After the last is incapacitated head down and talk to the Doctor and the Male Nurse to learn that the other Doctors are in danger. You get the three added as additional objectives, but before you head out looking for them, turn to the left and go to the office towards the back right corner of the room to grab the Patient Interview tape for The Riddler, which you then get to listen to.