Eradicator/The Backdoor (0A)

Kamchak Intro: The Backdoor (0A)
You begin your mission in a courtyard where you've landed. Go up to the overlook and enter the complex. The doors at the far end of the main hallway are locked or unpowered at present. Go to the side passage that was to your right when you came in, and up the ramp to a control room. Find and hit the switch to power one of the two doors. (There's ammo in that nearby side room that overlooks the courtyard.) Near the switch is a grating on the wall. There's a secret area inside.

Bonuses
A side excursion: Go inside the door opposite the side passage, to a warehouse. There's lots of ammo in here. You'll see a Mazrium platform alongside a stack of crates opposite the door. Look in a corner of the room for a switch that turns on the platform, then take the platform to the top of the crates and collect the Geosurvey. When you stand on that blue crate where the Geosurvey was, it briefly opens a concealed door here in the warehouse that was off to your right when you first entered. The teleporter inside leads to the control tower outside, which is a secret area. Back in the warehouse, look on the wall opposite the door for a discolored patch. It's off toward the left. Shoot it open for another secret area.

Exit
When you're done in the warehouse, go to the end of the main hallway and take the unlocked door to the power room. Hit the switch at the opposite end to power the other door in the hallway. Go in that door, and hit the switch in the room inside to open up the entrance to the mine tunnel, which is here in this room. Head down the tunnel and enter the Citadel.