On this page of the Far Cry 6 guide, you will find a detailed walkthrough of The Legend of La Princesa treasure hunt available in Madrugada.
The Legend of La Princesa
Subregion: Costa del Mar.
District: Espiritus Cay.
To start the treasure hunt, you must read the note attached to the wooden pole.
Your task is to go to a cave that is under water. It is worth noting that the character does not have very capacious lungs - you will quickly need to catch your next breath. Keep this in mind when exploring the depths.
Head for the jellyfish that swim underwater. Remember to not get too close to them, or they will electrocute you.
You will come across a skeleton that has a note next to it. It will help you learn more information and get a few clues. These, however, may not be entirely clear.
Making the task easier. Simply look up. There you will find a point to attach the rope. Climb to the floor above - it is not accessible in any other way.
Climb up the rope and jump to the rock platform.
Now all you have to do is run upwards - you will come across a chest. Open it to complete the task.