Balloon 16 (Industrial District)
This balloon is on the arm of one of the two nutcrackers on top of the Steel Mill.
Balloon 17 (Industrial District)
At street level, you should look for the “Joker’s Funhouse” sign that has been repainted to say “Harley” above a tunnel entrance. Inside, to the left of the track, you’ll find a balloon.
Balloon 18 (Industrial District)
Just east of the green objective marker, you’ll notice a tower with an antenna, a nutcracker statue, and a balloon.
Balloon 19 (Steel Mill, Loading Bay)
As soon as you enter the Steel Mill, walk forward a bit and look for a crib to your left.
Balloon 20 (Steel Mill, Loading Bay)
Look up at the hanging cop, then look to his right. You’ll spot a balloon attached to one of the steel support beams.
Balloon 21 (Industrial District)
After hacking the console which opens the door to Harley’s secret lair and passing through the raised door, you’ll notice a balloon in the hand of the Harley statue to the right of the entrance to the Shipyard.
Balloon 22 (Shipyard, Pump Room)
Use Batman’s Line Launcher to reach the southern area of the map. At the top of this staircase, you’ll find a balloon.
Balloon 23 (Shipyard, Warehouse)
Climb up the winding stairs until you reach the section that is broken. Instead of climbing into the nearby duct, look up instead near where the steps continue to find a balloon.
Balloon 24 (Shipyard, Warehouse)
In the room where you find the tied-up cop, look for some lockers in the northeastern corner of the room.
Balloon 25 (Shipyard, Warehouse)
In the room where you find the tied-up cop, check the west side near the “Shrine of Joker” sign to find a balloon.
As Robin (The Second Time)
Balloon 26 (Shipyard, Joker Shrine Room)
Immediately upon entering the Joker Shrine Room as Robin, you’ll see this balloon.
Balloon 27 (Shipyard, Joker Shrine Room)
Upon entering the main room in the Joker Shrine Room, simply look up at the ceiling to find a balloon near the crane hook.
Balloon 28 (Shipyard, Access Corridor B)
Use the floor duct to go underneath the malfunctioning door. When you emerge, you’ll have a sniper to your right and a balloon to your left, on a barrel. Take out the sniper first (if you need to).
Balloon 29 (Shipyard, Access Corridor B)
Once you enter the angled (in terms of the map) hallway leading from Access Corridor B to the Dry Docks, immediately turn left and look in the corner to find a balloon.
Balloon 30 (Shipyard, Dry Dock)
After clearing out all the thugs and incapacitating Harley, head to the southwest corner of the Dry Docks and look for some water. This last balloon is just a few feet away from a large brown canoe.
If you want more balloon-popping, penguin-punching, Riddler-riddling collectible fun, check out our Batman: Arkham City Riddler guide. It has the solution to every Riddler mystery, physical challenge and the location of every collectible.