In the room with the two waterfalls (for lack of a better word) look up. There is a point where you can use your grapple.
Use your explosive gel to destroy the structural weakness guarding these trophies. Crawl under the door, step on the panel, and hit the Riddler switch that turns on behind you. This will open the cages, but it will also release steam from the six vents in the room. Use your freeze blast to stop the steam before it kills you. After you close all six vents you’ll be able to leave the room.
In the room with the two waterfalls, chuck a freeze blast into the water to create a raft. From the raft, you can spot this trophy on the wall. Use your Batclaw.
There’s a gate blocking you from this trophy. The gate is controlled by the fuse box beyond it. Run south down the tunnel until you find some electric arcs running across the ceiling. Pilot a remote Batarang through them and all the way back into the fuse box.
“Which notorious family keeps talking trash?”
“Can you find this cool couple before the romance thaws?”
Inside the building in which you find Nora Fries.
“This question can only be answered from an unusual perspective. Can you get yourself there?”
Stand on the chimney of the same building where you found #2 and look west.
“Breaking news! Get out while you still can.”
“If you’re planning on making a mark in Arkham City, you’ll need a special kind of realtor.”
Inside Zsasz’s hideout.
“Was this parasite ratted out, or does he continue to plague Gotham?”
“Air, sea or land. It would be criminal not to use these wise guys, wouldn’t it?”
“Does Zsasz still pose a threat? This guy called to find out.”
“Did you hear the HOLE story of how Black Mask escaped?”