Treasure Hunter in Dying Light 2

The quest will start automatically after the Deserter mission if you choose to save the map. The reward for this quest is 500 combat points, 1500 parkour points, and two remote explosives.

You need to decipher the note to understand where the treasure is hidden. Take the ship down to the library and chat with Albert. Interact with the book on the table to find out the cipher, and then examine the note next to the book. It has a code on it.

You need to go to Muddy Grounds, to the basement of the water tower, and enter the code 03-21-67. Head to the tower in Muddy Grounds, go inside and drop down into the flooded basement. Look for the safe under the coasters and enter the code 3-21-67. Take the explosives.