Great Swamp
The Great Swamp is a place in A Link to the Past, the Great Swamp is, as the name implies, a large swamp. The grass there hides armed soldiers and mines. To the south is the Swamp Palace. The whole place was flooded and now lies in ruin.
In the Light World the cave near the north entrance has a Fairy that will restore Links health. At the north west there is a portal to the Dark World which can only be accessed after Link has obtained the Hammer. Just below the portal there is a whirlpool which the River Zoras allow Link to use to transport around Hyrule. The ruins at the south can be entered and by pulling the right lever, the water from around the outside of the ruins will drain and a heart piece will be available. A fish will also be jumping about and if Link picks it up and throws it into the water the fish will reward him with 20 Rupees.
In the Dark World the ruins are the location for the second crystal. Known as the Swamp Palace, the item found there is the Hookshot and the boss of the palace is Arrghus.