Nora Fries is Mr. Freeze’s wife and is used by the Joker in Batman: Arkham City to coerce Mr. Freeze into making a cure for the Titan disease.
After the fight between Batman and Mr. Freeze in the GCPD building, the side mission Heart of Ice is unlocked. It marks a big blue circle on the map of the Industrial District which could also be the potential location of Nora in Batman: Arkham City.
To find Nora Fries, glide down to the boat under the bridge connecting Amusement Mile and Industrial District in Batman: Arkham City. It will be next to the red “North Gotham Docks” neon sign. This is roughly in the top left of the big circle.
There is a large destructible wall in front of the boat. To get close, throw a Freeze Blast to create a floating platform on the water. Jump onto it and use Batclaw on the metal rings of the wall to tug yourself closer.
Detective Mode can be used to identify walls with structural weaknesses – they will appear as glowing purple.
Use Explosive Gel to break open the wall and advance through the door to enter Storage Warehouse 5B.
Propel yourself into the vent in front of you which will take you under the enemy’s lair. You need to fight off the thugs above you to progress.
Start by performing a takedown on the one directly above and then clear out the others. Be careful since there are a few armored and shielded ones in the group. Use your combos to take them down effectively.
After defeating the thugs, scan your surroundings to find Nora. She will be in a container on your right, safe and alive.
Head back from the main door; you need your Cryptographic Sequencer to open it. The password of the door is FROZENBAIT.
Once you are out, return to GCPD to report Nora’s location and status to Mr. Freeze in Batman: Arkham City. You can find him in the Forensic Lab on the bottom-most floor where you defeated Mr. Freeze.