WHERE IT STARTS:
Head over to the Treasure Map Start Area in the south east from Camp Maximas, Balaceras, Valle de Oro.
It starts NORTH OF BURROS BAY, Cruz del Salvador, Valle de Oro.
Look for an orange box inside a little shed.
THE NOTE SAYS:
"Rosa, muse of my heart, has vanished and she's taken the key to my heart with her. Oh, Gods above and below, Rosa was the only one who could show me paradise!
There is a King's ransom for anyone who can tell me where she is.
Now, as I am a master of the language arts, I feel the need to stoop and make myself clar that by 'heart' I mean 'my valuable sh**' and by 'key', I mean 'an actual key'.
F*** this, I'm going to the bar.
Ambrosio Pedro Cartagena, (former) Poet Laureate of Yara"
WHAT TO DO:
Written Guide below the Walkthrough Video
After reading the note, you should get a search area on the minimap.
Pretty quickly you should realise, that all the boats have names.
Go to the bar first - To the top floor, where Ambrosio left a note.
Take the key that is hanging at the board with numbers on the wall.
You'll need that.
And then, on a little lookout in the search area you will find a note of the poet, that his boat 'Rosa' sank and he can't swim.
Look out to the sea. There is a buoy.
Dive down to the sunken boat and open the big bright chest.
Reward: Dark Tech Mask