This achievement is story-related and will unlock after the 3rd Catwoman intermezzo.
As soon as you take over control, go to the mission marker and enter the building. Inside the building, you have to steal 3 keycards. After that go back and use the computer to open the vault. A fight will start and after said fight you are free to go into the vault. Take the briefcases and the achievement will unlock
(video credit: Batman Arkham Videos)
Hope this helps!
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