At the beginning of the stage, jump into the water and head into the deep end. Dive down and look for the cave opening, which will be marked by a ring of coins. This will be your destination, so swim until you get out of the water in the cave. You won’t find much in this cave, but there is a Blue Coin Block here, so keep that in mind for the 100-coin star. There will also be pillars here that fall down whenever you get close, so be aware of getting smashed by one of them.
On the far end of the cave will be your goal, where you’re presented with another four chests. These are similar in nature to the ones found in [Plunder in the Sunken Ship], as you will need to open them in a set order. When looking at the chests with the rest of the cave behind you, open the chests in the following order:
- Back, left, right, front
Upon opening the final chest, you will get yourself another Power Star.