WHERE IT STARTS:
There is the GRAN FINCA POWER STATION at the bottom of the CIELO GARDENS CHECKPOINT, NOVENTARMAS.
Interact with the orange box.
THE NOTE SAYS:
"NOTICE OF TERMINATION
I told you. I warned you, but nobody listened. After all, I'm just your manager! Does chain of command mean anything to you?
So now thanks to you, all employees of the Gran Finaca Power Station have been TERMINATED for entering my office and messing with my valuables.
It is also my obligation to inform you that any attempt to access the building will result in legal action.
WHAT TO DO:
Written Guide below the Walkthrough Video
Based on the note, you need to find the office.
Walk around the building and you will see a grapple spot. Go down there and follow the way inside the building.
You have to turn the power on to open the big gate in this room.
To do so, you have to go into the flooded area. There are 2 pipes to either melee hit or shoot.
Get inside and swim to the left above the water. Then dive down to get to the first pipe. Hit it.
The water will go down and you get access to a ladder that goes further down.
There, you can shoot or melee the second pipe.