The Forsaken Fortress is an unusual location in The Legend of Zelda: The Wind Waker for the GameCube. It's considered both an island and a temple. Link, the game's protagonist, will come here many times on his adventure, and if the player wishes to complete all the side-quests he'll even have to do so more times.
There are two sidequests that the player can partake in in the Forsaken Fortress. The first one will nab you a piece of heart (Piece of Heart #1), while the second will give you a Silver Rupee (via the 25th Treasure Chart). The piece of heart can be found in room 1 of the first floor. You don't need any fancy weaponry to get this - on your first way through the dungeon you can get it for yourself. The Silver Rupee can by caught by simply following the instructions of the 25th Treasure Chart.