Fast travel to the Gold Coast.
Go to the man on the docks not far from whee you spawn.
Next you will be required to kill a random NPC within this DLC area. I advise doing it away from any guards.
Return to the spot where you talked to the man that told you to kill the NPC, another NPC will show up.
Now make your way to the light house by swimming or traveling the curved coast.
You'll talk to a NPC inside and half way through the conversation you'll get this achievement.