Diamond Steppe Island (A6 on the map) is one of the 49 different islands featured in The Legend of Zelda: The Wind Waker for the GameCube. The island is in the shape of a diamond if viewed upon from above. There are various sidequests that you can be a part of here.
One of the sidequests is defeating the Big Octo that resides here. It has eight eyes, all of which can be hit using Link's boomerang (note: Link can target five eyes at one time). After all of the eyes are hit, the Big Octo will die, giving Link access to the treasure he leaves behind - an Orange Rupee.
Using Treasure Chart #23 will give LInk access to the Piece of Heart #11. On the island the player can find a Blue ChuChu, who should be defeated in order to get Blue Chu Jelly. You'll find a hole at the top of the island (note: in order to get around you'll have to make use of your Hookshot) that'll lead to a Ghost Ship Chart. Finally, when the moon is in its gibbous stage at night time, a Ghost Ship will appear next to this island.