WHERE IT STARTS:
Head over to the Treasure Map Start Area in the very north of NOVENTARMAS.
The orange box is inside, on the table.
THE NOTE SAYS:
"TO: ALL PERSONNEL
SUBJECT: NOTICE OF IMMEDIATE ACTION
Maria Marquessa has a ZERO TOLERANCE POLICY for Fake Yarans, loiterers, vagrants and, especially, squatters on her property.
The previous owner of this property absolutely cannot lock themselves in the premises and expect a civil response.
You are hereby ordered to hunt down and remove this individual using any means necessary. Ensure that you respect the property and that it does not suffer from too much damage in the process.
I suggest you begin your search by checking their former office. Finally, remember to reclaim any valuables they have stowed away.
WHAT TO DO:
Written Guide below the Walkthrough Video
After reading the note, go to the room with the tanks.
There is a big tank with 3 red lights.
Find and use the 3 valves in this room, then turn the valve on this big tank with the lights.
After the explosion, look up and use the grapple to get up.
Go through the vent to the other end. You've reached the office.
The chest is upstairs. So is the keycard for the door to exit.