Complete the indicated task to access the corresponding uncharted island.

Cliche Island
Collect the five pieces of Captain Taint's map. Start the quest to help him get his treasure. He tells you it is on Cliche Island and that a Mutinous Captain may have it. You can also find Mutinous Pirates with the captain on X Island. Just west of X island is Chicken Island, which has the parrot feather required for a different quest. Start at the dock at Chicken Island, then move straight west until you see a small island slightly to the north. Dock there to find Cliche Island and a treasure chest.

Hot Island
Move south from the western side of Spider Island.

Skull Island
After invading the North Pole, get on your ship and travel south from the dock. Look for a few rocks sticking out of the water and a spear with a skull on it.