On this page of the Far Cry 6 guide we've described a treasure hunt - The Last One to Leave - available in the Esperanza region.
District: Roja Bay.
To begin the treasure hunt you must read the note on a metal part, right by the building's door.
Start by heading to a blue house, east from the area you took the quest in. Enter it through the door. Inside there's a switch you must use.
Now you need to climb up the metal flagpole, on which you'll find yet another switch. You can get here by making a running start jump off the nearby roof.
The last switch is in a house on the hill, go through the broken door to reach it.
Here you'll need to finish a task. You must use the items in the correct order to open a secret passage. Turn on the radio, then the TV, then twist the picture hanging by the bookcase.
Once the passage opens, flip the switch to open the door and finish the task.
Time to wrap it up. Return to the quest's starting point, open the door and examine the chest. You'll complete the mission.