In Just Cause 4 there are some hidden tombs, in these tombs you have to open the entrance to a secret room. In the chamber you have to light a candle to read a hidden text.
In total, there are 6 Tombs you must solve before you unlock the tomb of Otorongo. The first grave (The Tomb of the Servant) should be revealed automatically, quite early in the game. The last Tomb is,The Lost Tomb of Otorongo.
By finding and solving all graves, you unlock the following trophy:
Knowledge is Power trophy
Uncover the mysteries of the Lost Tomb of Otorongo
All Tomb Locations & Solutions
To unlock the Tomb and mission of Otorongo, you must find all the Tombs. Each tomb has a secret chamber with invisible lines on the wall. If you have a chamber open, you have to light a candle to read the lines.
So you unlock the last tomb, you must have read all the hidden texts. There are six Tombs in total:
The First Tomb you get automatically, it is a part of the Story - Tumba Del Sirviente
The Tomb of the Princess (Tumba De La Princesa)
Tomb of the three children (Tumba De Los Tres Ninos)