Cat Quest III

The Purrmaid can be found in the Sunset Islands to the north of the map. You will need to approach from the north side of her small lake and shoot a barrier with the ship to speak with her. She will give you the Shell Phone which allows you to get treasures buried at sea. You may have noticed the whirlpools that you can interact with but until now nothing happened. There are eight of these to find. Once you collect the treasure from all eight whirlpools, return to the mermaid to complete the quest and unlock the achievement. The locations can be found HERE or by following the video below.