In the previous part of the walkthrough, you used the climate analyzer to help you locate the coldest part of Arkham City. This took you to the GCPD which you believe Mister Freeze is using as a hideout.

Head down the corridor. Locate a ledte to the top and grapple up there. Jump to the far wall and find the grate, open it and crawl inside. Keep going in the ducts until you reach a big room. There will be 5 armed hostiles in the room. Take them out cautiously. One wrong move and all of them will shoot you, killing batman.

And i that's not enough, Penguin's keeping track of his crew using heartbeat monitors. He will know each time you take someone out. You need to move quickly.

The thugs realize that you are in the building and let Penguin know. Penguin tells them to keep you busy and that he has shut down all access to the GCPD so you are not going anywhere.

Use drop attacks to silently kill thugs without other noticing. If you do get spotted, use smoke bomb and move fast across the room until they lose sight of you.

In the end the last inmate will give up, drop his weapon and surrender. Interrogate the surrendering Thug. You will ask him where Freeze is. He will tell you that Mister Freeze is in the Museum and that Penguin has got him.

Your objective now will be to Rescue Mister Freeze from Penguin in the Museum. The location of the Museum will be added to your map.

But first you have to find a way out of the Gotham City Police Department. As you approach the exit, Penguin locks you in.

Alfred will contact you to ask if you got the cure from Mister Freeze. You will tell him that Penguin has Freeze and that you are trapped in the GCPD building. Alfred will warn you that you will die if you dont get the cure soon.

You will download unlock codes for the municipal structures. The batcomputer should say "Downloading Gotham Municipal Codes".

Use detective mode to track the wires back to the security gate control. You might have to go under some ducts below. When you reach the control (a terminal with a picture of a lock on it) prepare the cryptographic sequencer. Use cryptographic sequencer to hack the gotham municipal network. Tune Passkeys to exchange key and crack the password. This will open the security door and you can leave the GCPD and start making your way to the museum.