Twilight Realm

"Some call our realm a world of shadows, but that makes it sound so unpleasant...The twilight there holds a serene beauty...You have seen it yourself as the sun sets on this world. Bathed in that light, all the people were pure and gentle...But things changed once that foul power pervaded the world..."

- Midna

The Twilight Realm is the name of a parallel dimension to the realm of Hyrule, a world of shadows and perpetual twilight whose only source of light comes from the two sacred orbs known as the Sols that are kept in a special shrine near the plaza of the Palace of Twilight. It is the homeworld of the Twili, a race of shadow-beings descended from the Dark Interlopers that were banished from Hyrule to this strange new world as punishment for their attempted conquest of the Sacred Realm in an attempt to seize the Triforce. In the aftermath of the Interlopers' banishment, they evolved into the Twili race. The only link between the Twilight Realm and Hyrule is a relic known as the Mirror of Twilight, which acts as the gateway between the two worlds. While the normal Hyrule resides in the World of Light, the Twilight Realm exists in perpetual Twilight, which is the absence of light. Not light in the normal logical sense, but in the spiritual sense. It is a realm in which there is no light, but Twilight. The Twilight Realm is a gloomy, hazy, yet very serene world. It is often called the World of Shadows, but that makes it seem unpleasant. There is a serene beauty to the Twilight Realm, a beauty which the Hylians have seen every time the sun sets, during hour of Twilight.

For much of its early history, the Twilight Realm was a peaceful place, until the King of Evil known as Ganondorf was banished to the realm by the Ancient Sages, where his evil influence would cause a coup of the government and cast the realm into darkness by overthrowing the true Twilight Princess and installing a puppet ruler named Zant into the position of ruler of the Twilight Realm. Zant would go on to seal away the Sols, leaving the Twilight Realm in darkness, and invade the land of Hyrule on Ganondorf's orders in order to merge the two worlds together into a single empire. After the Dark Lord's defeat however, peace was restored, and the Twilight Realm was truly free of his grip. This was made possible by the efforts of the Hyrulean Hero Link and Hyrule's Princess Zelda, before the Mirror of Twilight was shattered by Princess Midna, the Twilight Realm's rightful ruler that was restored to power. This action severed the only known road between the two worlds, desroying the only known means of travel between them to prevent similar events from happening again.

History
The Twilight Realm's full history is incomplete, leaving only a brief bit of its origins and its recent history as the only available information regarding its past.

Origins
At a certain point in the history of the land of Hyrule, a war broke out across the land when a group of shadowy magicians known as the Dark Interlopers learned of the mythical Triforce located within the Sacred Realm and attempted to establish dominion over it to harness the Triforce's power. To this end, the Interlopers crafted an ultimate weapon, the dark relic known as the Fused Shadow, inside which they had vested a vast amount of their magic.

When the Interlopers seemed on the verge of victory in this effort, the Golden Goddesses decided to order the Light Spirits of Hyrule to intervene and seal away the dark magic of the Interlopers to halt the war. The Light Spirits, at the order of the goddesses, shattered the Fused Shadow into four fragments (hiding three of them across Hyrule and leaving the fourth in the hands of the Interlopers) and drove the Interlopers across the land of Hyrule into the twilight. They were then imprisoned within the Twilight Realm and lost their ruler as punishment for their greedy actions that sparked the war.

In addition, the Twilight Realm's effect of causing those that dwelled within it for an extended period of time to only be able to exist as shadows outside of it took its toll on the Interlopers, dooming them to this fate as well. Over time, the Interlopers would evolve into the Twili and reestablish their monarchy that would come to rule over the Twilight Realm. The goddesses did not completely sever the Twilight Realm's connection to Hyrule however, for they left a lone link between the two worlds in the hands of the Ancient Sages, the Mirror of Twilight, which could only be shattered by the true ruler of the Twili.

Trivia

 * The Twilight Realm originally had a flat, monochromatic look. This early version of the Twilight Realm was featured in several trailers for before it was revamped before release.