Where to find the Royal Burial Ground
Once you've managed to sink the Royale Louis, loot your rewards and get ready to sail southward. Here's what you need to do:

Open the world map and check the journal so you can inspect the clue regarding Caradec's Bounty.
The document refers to the Royal Burial Ground, which is an outpost along the southeastern portion of the Red Isle.
If you haven't visited this area yet, make sure you disembark once you're close enough to Skull and Bones Items turn it into a fast travel point.

Caradec's Buried Treasure location
The next step in the High Seas Heist quest in Skull and Bones involves looking for buried treasure. Based on the first clue, we need to find a tree that has an hourglass-like marking. Simply head up the sloping path from where you disembarked. You should spot the tree in the clearing, and a glowing beam will appear to cheap Skull and Bones Items denote the area where you can dig.