Arkham Island - Batman: Arkham Asylum
If you go into Detective Mode here, you will notice some enemies off to your left, and ahead of you across a big gap you should see a duct grate highlighted in orange.
There are a lot of guards/cops outside, and you should talk to a few – like Louie Green – for some backstory and to add to the whole You Are Batman! deal. When you are done doing that head towards the two enemy for a quick CS with Oracle about your car – and get a map uploaded from her that covers the entire island.
Your new challenge is to protect the Batmobile, which is now highlighted on your new map, so head towards the gate and talk to the cop there, then if you like, the cop by the ambulance. On the other side of the ambulance are the two bad guys – and you might be tempted to climb on top of the ambulance since it offers to let you do that... Don't.
To the left of the front of the ambulance above is a Zip Point – go ahead and zip up to that, as that will put you above the bad guys. Now simply ninja drop behind them and take them out using silent Navy Seal Ninja Kills!
As you walk through the next gate you will notice that there are some towers – one to the right above – and one in the distance, and there is a group of unarmed prisoners attacking the Batmobile. Zip up to the tower on the right then do a glide-kick to take one of them down, and engage the group in combo-attacks. Taking these guys down should be a piece of cake for you by now!
Once they are defeated you get a prompt to grab some explosive gel out of the boot – would have been nice to have this back in the Asylum, right? But you have it now, that is what is important. You may also have noticed that with each new sub-area you enter there are new Riddler Challenge Riddles – you can try to solve those if you want to, I chose not to because a lot of them require skills and items I do not have at the moment.
--=--= About Riddles =-=-
Obviously if you are intending to 100% the game, you are going to want to solve all of these, but you will find it a lot easier if you simply wait until you have finished the game, and then after the credits, hit continue to go into Free Play mode. Now you can backtrack and complete all of the Riddles, get all of the collection items, and complete the challenges you did not do on the first play through. We've covered all the riddles as a seperate section at the end of this guide
You will find it a lot easier to do it this way than to try it when you are not really prepared for the difficulty of some of them. Still it is your call!