Atlantis is a seemingly mythological island, presumably big enough at its height to be considered a continent, that was regarded as the most advanced civilization in human history. According to Plato, a Great Flood sank the entire city into the Atlantic Ocean "in a single day and night of misfortune." It is the main setting for the film Atlantis: The Lost Empire.
History
The city is saved from complete destruction from the Great Flood.
Sometime presumably before 100,000 BC, Atlantis was simply another civilization in the world and the Atlanteans were a normal race like any other. One fateful day, a huge comet passed over the Earth. A single piece broke off and fell upon the landmass that was inhabited by the Atlanteans. To their astonishment, they managed to discover the great properties possessed by the comet fragment. Soon, they would use the fragment, which they called the Heart of Atlantis, as their source into becoming a more advanced civilization than any other.
But instead of using their new found technological powers for good, they exercised it to dominate other lands. They created a fearsome armada of flying machines that waged war with unmatched strength. However, their hubris would become their undoing when an accidental discharge caused a Great Flood that threatened to wipe out Atlantis as a whole. The crystal that had fueled their technology and gifted them with extended longevity, would save a part of the city, though it would be buried beneath the waters and deep into the Earth.
Humbled by the result of their arrogance, the elder leaders of Atlantis, in particular its King Kashekim Nedakh, decided to keep the crystal secret, even from its people, forever so as not to repeat their actions. Kashekim went further by ordering all of Atlantis' history to be destroyed and hid the crystal deep within the city through the throne room. Overtime, their past glory had been all but forgotten.
Atlantis rediscovered.
At some point, a shepherd named Aziz managed to stumble upon Atlantis. For two years, he secretly immersed himself it its culture, uncovering bits and pieces of its past, including the location of the Heart of Atlantis. Upon his return to the surface, however, he was considered a madman and subsequently sent to an asylum. While imprisoned, he would detail his journey in great detail, albeit in the Atlantean Language. His writings would become known as the Shepherd's Journal.
The Journal would pass through many hands over time, thus bringing the legend of Atlantis back into the consciousness of the surface world. Some considered it fact, others called it fiction, the discovery of the lost empire was nonetheless considered one of the greatest treasures all archaeologists strive to achieve.
In 1914, Preston Whitmore funds an expedition to Atlantis following the recovery of the Shepherd's Journal three years prior. Under the command of Lyle Rourke and guided by Milo Thatch's translation of the book, the expedition succeeds in finding Atlantis, despite suffering a loss of well over half its crew.
Rourke attempts to steal the Heart of Atlantis after he manages to locate it, uncaring that to remove the crystal from the city would bring about imminent death to its people. Milo leads an effort to stop Rourke and returns the crystal in time to avoid the city being engulfed by lava form an erupting volcano. While the expedition returns to the surface, Milo stays behind the help the people rediscover their past and lead them to a better future.
Geography
According to Plato, Atlantis is located somewhere beyond "the pillars of Heracles." The exact position has been debated by scholars for centuries with no theory being any better than the other. Many have even reasoned that it may not be in the Atlantic Ocean as has generally been believed.
The city manages to thrive underground.
At the height of it's power, Atlantis was, as Plato described, "an island which was larger than Libya and Asia together." Following the Great Flood, all that remains is a small island that has been buried within the Earth. Despite being a fraction of its once enormous size, Atlantis is still a very large city, comparable to the size of the major cities on the surface such as New York City, Paris, Tokyo, and London.
The journey to Atlantis is a difficult venture unto itself. One must first descend toward a specific point in the Atlantic Ocean. Travelers must then successfully pass a Leviathan to an underground tunnel it guards. Upon surfacing into the entrance of a cavern, travelers must trek for days through the catacombs of Atlantean ruins. Finally, there is a dormant volcano they must pass before reaching Atlantis.
What remains of Atlantis is situated atop flowing lava, protected by the power of the Heart of Atlantis. While the city is mostly ruins, it is still vibrant with life. Following the events of the city's rediscovery by the Whitmore Expedition, the Guardians of Atlantis previously thought to have been lost in the Great Flood have surfaced from their dwelling beneath the city's waters and stand in an encompassing circle, signifying the range of their protection. The Heart of Atlantis, once hidden deep within the city, now shines above, hovering over the city.
Development
Concept design of Atlantis with notes by Mike Mignola.
The filmmakers noted that the vast majority of their research about Atlantis was primarily done through the Internet. Sifting through all of the information they could find, both plausible and fictitious, to pick out what would work to facilitate the story they were telling.
For the visual design, directors Kirk Wise and Gary Trousdale immediately did not want Atlantis to be heavily influenced by the commonly used Greek look. Art director David Goetz noted that, as part of the desire to illustrate the civilization as being the "mother culture," they looked into the unsual architectural designs used in Southeast Asia, notably Cambodia, as well as the Myan architecture found in South America. Further refinements were done in an effort to emulate the art style of production designer Mike Mignola.
The core production team took a trip to the Carlsbad Caverns National Park in southeastern New Mexico during the pre-production stages of the film. This was done for research to get a better feel of what it is like to live underground. It also provided inspiration towards the development of the caverns the Whitmore Expedition journeys through towards Atlantis.