This achievement is story-related and cannot be missed.
When you are searching for Ras Al Ghul you'll eventually find yourself underground Arkham city. Right after the predator sequence in Wonder Tower Foundations you have to go through a tunnel-like passage and open doors with your shock rifle. You'll be attacked by some female Ninjas. Take them out and continue going forward. The achievement will unlock as soon as you leave the tunnel section and enter the next larger area which contains Wonder city.
(video credit: Batman Arkham Videos)
Hope this helps you guys!
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