Swamp Palace (A Link to the Past)

The Swamp Palace, also known as the Watergate Dungeon or the Flooded Palace, is the second dungeon in the Dark World in A Link to the Past.

Entrance to the Palace
The palace is located in the area south of the Bomb Shop in the Dark World, known as the Plains of Ruin. While Link can enter the dungeon, he cannot progress beyond the first room until he first returns to the Great Swamp of the Light World and enters the Swamp Ruins, the Light World counterpart to the Swamp Palace. In there, if he pulls a switch to drain the water from outside into the ruins, he will also cause water to flood the first room of the Swamp Palace. If Link has the Zora's Flippers, he can then travel deeper into the dungeon itself.

Themes and Navigation
Most rooms feature water to some extent, and others even have underground waterfalls. This is the first water-themed dungeon in the Zelda series, thus initiating a well-known type of complex dungeons appearing in later games, with successors like the Water Temple in Ocarina of Time or the Great Bay Temple in Majora's Mask. The Swamp Palace itself is not quite as complex as later water-themed dungeons (and certainly not as complex as later dungeons in A Link to the Past) as Link is not forced to travel under the water itself: it merely requires Link to fill certain passageways with water so he can then swim across. Link must be cautious in this dungeon because the watery amoeba Kyameron will rise out of the shallow water and hurl themselves at him, bouncing off the walls in an erratic fashion, and the swarming Pirogusu can sap at his strength in the shallow water that fills almost the entire dungeon.

The main treasure is the Hookshot, making it's first appearance in the series. This item's chain allows Link to reach previously inaccessible places, and it and similar hookshot-like items go on to appear as treasures in many water-themed dungeons, such as the Catfish's Maw in Link's Awakening and the aforementioned Water Temple, among others. The end boss is Arrghus, a giant one-eyed jellyfish protected by Arrgi. After defeating him, Link receives a Heart Container and the second Crystal.

A Link to the Past comic
The Swamp Palace is also featured in the A Link to the Past comic. When Link and Epheremelda head out to the palace,they discover that the area is completely dried up. Link calls to Sahasrahla via the Comm-Fork for help  and asks him to go to the Light World location of the Swamp Palace,   where Sahasrahla and the boy accompanying him find a fountain  surrounded  by statues. The boy, able to see Link in the water of the fountain, warns Link of the monsters behind him, where a Hinox and a Tarosu shut the door to trap the young hero inside the palace. As the boy watches the battle between Link and the foes, he  accidentally activates the statues that cause water to pour into the   fountain. This leads to the Swamp Palace in the Dark World to get  flooded, washing away the monsters and Link.

The Hinox and Tarosu end up sinking as they struggle with each other, while Link's Master Sword is dragging him below the surface. Epheremelda tells Link to stay afloat, for the water is almost up to an opening that the fairy had found earlier on. The young hero is then rushed into a new chamber, where he finds the  second maiden imprisoned in her crystal. As Link makes his way to the  maiden, a large, tentacled monster attacks him. He thrusts himself with  the Master Sword into the monster and defeats the creature, which  spits  out Link from inside and gives him a chance to destroy the  floating  crystal where the maiden is. The maiden, now freed, thanks Link and  tells him that Zelda is imprisoned in a rock shaped like a turtle found at the end of the world, then vanishes.