This is a side quest. You can get it in Trench Town. You'll need to speak with Lucy down in the slums and she'll ask you to help out her "friend" in the Wreckage Zone. The main goal is to open up 3 doors in the bunker in the Quarry.
Hope this help.
Thanks to Gerbasgamer to precise :
To start the mission look for the hanged guy near your camp.