Dark World

The Dark World is a dimension parallel to Hyrule, which is referred to as the Light World in contrast. It has seen two appearances in the Legend of Zelda series. The Dark World debuted in A Link to the Past, making it the first of many realms alternate to Hyrule to appear in the series. Though Four Swords Adventures also a features a Dark World, it does not seem to share a connection with the one in A Link to the Past.

A Link to the Past
In A Link to the Past, the Dark World is a fully explorable Overworld. Once the Sacred Realm, or Golden Land, this world was twisted when Ganondorf claimed the Golden Power, or the Triforce. Its layout is very similar to the Light World’s, but there are notable differences. It contains many of its own unique locations, namely a large structure at the Dark World’s center called the Pyramid of Power. Everything in the Dark World, naturally, appears darker. Many structures and buildings are in a state of disrepair, specifically in the Village of Outcasts. All the grass is brown and withered, and the water is an unnatural jade color.

Even the world’s inhabitants are warped, due to Ganon’s power over the Triforce. People have turned into monsters like Moblins or Hinox, anthropomorphic animals like foxes or frogs, unidentifiable creatures, and even trees. Even other creatures from the Light World, like Cuccos, take on more sinister forms here. While the Sacred Realm normally changes to reflect the heart of the one who enters it, the Dark World seems to have a reverse effect. The form that living things take in the Dark World is a reflection of what is inside their hearts and minds. When Link first enters the Dark World through a Portal on Death Mountain, he is transformed into a helpless rabbit, perhaps an indication of his pure nature. However, if Link obtains a Moon Pearl from the Tower of Hera, he can keep his true form even in the Dark World.

Around Hyrule, there are many magical transporters that lead to the Dark World, but entering these portals is normally a one way trip. Hearing legends of Golden Power, many people sought after it and became trapped in the Dark World. While most are trapped in the Dark World, Link can return to the Light World through the aid of the Magic Mirror, given to him by a lost old man for guiding him to through a cave. The Magic Mirror transports Link from the Dark World into the Light World. After using the mirror, it leaves behind a portal in the Light World so Link can return to where he left the Dark World.

History
In the event that the Hero of Time failed to defeat Ganondorf after he obtained Triforce of Power, the evil king stole the Triforce of Courage from Link and the Triforce of Wisdom from Princess Zelda. When Ganondorf obtained the complete Triforce, he became Ganon, King of Evil, and Princess Zelda was forced to unite Hyrule’s citizens to seal Ganondorf inside the Sacred Realm. Several years later, the seal on the Sacred Realm weakened, and many who had heard legends of the Triforce sought out the "Golden Land" and disappear inside it. With the power of the Triforce, Ganondorf transformed the Sacred Realm into the Dark World. In response to the impending threatened, the seven sages, as ordered by the King of Hyrule, began to seal the Dark World. To stop the sages in casting their seal, many monsters rushed forth from the Dark World's entrance, but Hyrule's bravest knights fought to protect the sages, many of them dying in the battle. They had bought enough time for the seven sages to successfully seal the Dark World, and that seal held for many ages. The battle became known as the Imprisoning War.

Many years later, the wizard Agahnim began capturing maidens, who were the descendants of the seven sages. One bye one, he sent them to the Dark World and used their power to weaken the seven sages' seal. Before he could send Princess Zelda, the final maiden, to the Dark World, she telepathically pleas to Link, who manages to rescue her from Hyrule Castle's dungeon, but it is only a matter of time before she is recaptured by Agahnim. Link rushes her to Hyrule Castle to save her again, but he instead witnesses Agahnim casting a spell as he send Zelda into the Dark World, finally breaking the seven sages'. Link confronts the Wizard, but before he could deal the final blow, Agahnim pulls Link into the Dark World.

Now in the Dark World, atop the Pyramid of Power, Link is telepathically contacted by Sahasrahla, the Kakariko Village elder, who informs Link of the connection between the Dark and Light worlds at the Hyrule Castle gate. Sahasrahla also prompts Link to save the seven maidens, as their powers can help stop Agahnim. After rescuing a maiden, she will share her knowledge with Link, who learns that Agahnim’s true intent was to free Ganon from the Dark World.. Link also finds out from the maidens that he may be the last of the line of knight who fought at the Imprisoning War, meaning he is destined to fight Ganon After saving Zelda from Turtle Rock, Link confronts Agahnim at Ganon's Tower and defeats the wizard for the last time. Ganon’s shadow is seen leaving Agahnim’s body, and it escapes to the Pyramid of Power. Link faces Ganon at the Pyramid of Power, and after a long battle, Link defeats him. With Ganon gone, the Triforce can now have a new owner, takes it in his hands and makes a wish on it to right many wrongs in the Light World, and the Sacred Realm is restored.

Four Swords Adventures
The Dark World of Four Swords Adventures is can be accessed and exited via Moon Gates, which Link can see because he holds the Four Sword, which also allows him to see inhabitants of the Dark World as shadows. Many Moon Gates require a Moon Pearl to be activated. While Link usually enters the Dark World through Moon Gates, he can also be force into it by a Floormaster. In the Village of the Blue Maiden, many children have been taken to it by “a dark shadow”. Through a Moon Gate, the Dark World appears hazy, and the shadows seen in the Light World now appear as physical objects; the music is even an eerier version of the current area’s theme. While the Dark World looks much like the normal world, many objects and buildings are moved around. This sometimes allows for Link to travel to places in the Light World that he could not reach without Moon Gates. While in the Dark, Link can lift his counterparts in the Light World and move them across gaps, which can be done to reach new areas and solve puzzles.

There is also an area in northwestern Hyrule called the Dark World, though it is different from the one entered via Moon Gates. This area contains the Lost Woods, Kakariko Village, and the Temple of Darkness. In search of the Dark Mirror, Link ventures here, where a cloud of darkness has covered Hyrule. It turned the [Lost Woods, once called the Forest of Light, into a dark place inhabited by fell creatures. While it is originally thought that this darkness was spread by Vaati and Shadow Link, who have been running rampant all over Hyrule, it is soon learned from Deku Scrubs in the forest that Ganon is its true source. When Link leaves the Lost Woods and travels to Kakariko Village, he finds that the town, and even many of its citizens, has been corrupted by the darkness. It can be assumed that the same would happen to the rest of Hyrule if Link does not save it. After aiding Kakariko Village, Link travels goes to the Temple of Darkness, where the Dark Mirror was hidden to keep it away from the rest of the world. After he clears the Temple of Darkness, he finds that the Dark Mirror has been taken, and it is the likely source of the many Shadow Links.

At the end of each stage is a barrier that can be broken if the four Links have obtained a certain amount of Force Gems. These barriers drain the Force from Hyrule, and if not destroyed, they would eventually transform all of Hyrule into the Dark World, because they are connected to it.

A Link to the Past comic
In the A Link to the Past comic, the events of the Dark World are heavily abridged: Skull Woods and Thieves' Town are entirely removed, and Link only saves two Maidens before rescuing Princess  Zelda in Turtle Rock. Though Link enters Misery Mire and the Ice Palace (referred to as the Ice Tower), no maidens are imprisoned there. Link cannot travel freely between worlds and is trapped in the Dark World once Agahnim transports him there. Moreover, the young hero maintains his form in the Dark World by controlling his emotions, while in the game the Moon Pearl is needed to maintain human form.

After failing to save Princess Zelda from Agahnim's clutches, Link kills Agahnim by deflecting his own magic, but Agahnim, with his final breath, manages to transport Link into the Dark World. Instead of turning into a rabbit when he stumbles into the Dark World like in the game, Link momentarily turns into a beast before suppressing his negative emotions and managing to stay in his human form. He then resumes his search for the princess, and befriends Epheremelda the fairy after rescuing her from monsters.

Helping Link out as a guide, Link and his fairy companion successfully free two Maidens from their crystals, with one of them revealing to Link that Zelda is imprisoned inside a rock that looks like a turtle. Link, with the help of Roam, a knight who is searching for the Silver Arrow in the Dark World, shows up and aids the young hero in defeating the monster in Turtle Rock. With Zelda now saved, the trio head to Ganon's Tower, where Ganon rises from the defeated body of an Agahnim specter. Link stuns the beast with the Master Sword, allowing Zelda to fire a Silver Arrow from Roam's crossbow and defeat Ganon. The Triforce rises from Ganon's body and asks Link to touch it with one wish in his heart as its new master. The Triforce transports them back to the now-peaceful Hyrule,with the Dark World vanishing and releasing all of the people who had been trapped there.