Great Swamp

The Great Swamp is a location in. It's a large area filled with grass and water ponds. The grass hides armed soldiers and mines. The Dark World counterpart is known as the Plains of Ruin and serves as the home of the Swamp Palace.

Features
The grass fields hide Agahnim's Soldiers and even mines, along with rabbit-like Toppo. There are numerous ruins in the area, it is unclear what civilisation they belonged to, however. In the Light World, the cave near the north entrance leads to a Fairy Fountain. At the northwest is a Warp Tile to the Dark World which can only be accessed after Link has obtained the Magic Hammer. Just below the portal there is a Whirlpool Warp which King Zora allows Link to use to transport around Hyrule. The ruins in the south contain a chest holding Bombs, but in the far room Link will run into a Bubble, along with two switches. One switch is a trap that will drop Bombs from above, while the other unlocks the watergate, filling the ruins and draining the water outside. Draining this water is key to accessing the Swamp Palace in the Dark World. With the water drained in the Light World, a Piece of Heart will be revealed. Fish can be found splashing about in the drained pond and, if Link picks one up and throws it into the water, the fish will reward him with a Red Rupee.

To the east of the area lies a canyon that serves as the entrance to the Desert of Mystery, while the southeast exit leads towards Lake Hylia. Travelling north leads to Link's House and Hyrule Castle.

Trivia

 * Toppos will cease to appear in the swamp once Agahnim has been defeated.
 * Even though Sahasrahla suggests that changing something in one world will affect its counterpart in the other, changing the water level in the marshes of the Great Swamp and its effects on the Dark World is one of the few instances where it is actually possible to directly influence one world from the other.
 * As well as obtaining Rupees by throwing one into the deep water, if a fish can be carried from the swamp all the way to Kakariko Village, the Street Merchant will reward Link if it is given to him.
 * Despite being called a Swamp in the English localization, more of the area is made up of large grass fields, with a few small ponds of water.