This page of the Far Cry 6 game guide contains a walkthrough of the "Passing The Torch" Treasure Hunt available in El Este.
Subregion: Sierra Perdida.
District: Promise Peaks.
To begin this quest, you need to read the note found on a tree. During this mission, you have to unlock a door. To do this, you must activate 3 switches that are hidden in the nearby houses.
Let's start with the yellow building. To reach it, you need to destroy the boards that block the entrance from below. Don't use firearms for this, otherwise you will have to wait for the fire to die down (we have tested this and assure you that it's not worth wasting your time).
Once you enter the small hallway under the building, look up and climb into the house. There you will see a switch hanging near the bed.
The next switch is located in a wooden building that can be used as a utility room. There is no door there, so you can get inside without any problem.
You can get inside the last building through the window. On its left wall hangs a switch that you need to activate.
Once you have activated all the switches, head to the open shed containing the last switch. This one will unlock the door to the building where the chest is located.
Upon entering the building, you will see a wooden box. Opening it completes the mission.