Maze Island

Maze Island is a geolithic labyrinth that exists in and  for drastically different purposes.

The Adventure of Link
Maze Island is a rather large island in Eastern Hyrule that, like its name suggests, is a natural labyrinth. Narrow passageways lined by unclimbable rock walls, impassable rivers with only the occasional bridge across them, and hidden pitfalls make traveling on this island both dangerous and time-consuming. Maze Island's single most famous landmark is the Maze Island Palace, which Link visits during his quest to wake the sleeping Princess Zelda.

The Kidnapped Child from the town of Darunia can be found here on the east side of the island, while a hidden Magic Container rests in the west.

Phantom Hourglass
In Phantom Hourglass, Maze Island can be found in the Northeastern Sea; it is initially unmarked. It contains three increasingly difficult mazes: Beginner, Normal, and Expert. To finish each difficulty level, it is required for Link to hit all the Gossip Stones that appear once the maze opens. Completing the Beginner difficulty (four Gossip Stones) gets Link a Wisdom Gem, and finishing the Normal difficulty (eight Gossip Stones) nets him a Treasure Map. Only by completing Expert (fourteen Gossip Stones) will the island relinquish its Heart Container.

There is also a Wisdom Gem inside a chest accessible by bombing a wall, as well as three Big Green Rupees hidden under the ground.