The Duat is the name given to the massive network of caverns running under the Greater Continent upon which Arindell sits. Because the dimension is flat, heat and pressure do not necessarily increase as they would beneath the surface of a round world.
The bulk of known or explored portions of the Duat are found under mountain ranges. Few, if any tunnels are thought to exist beneath the plains regions of the Greater Continent. The tunnels are thought to extend under all mountainous regions, though they have not been explored.
No one knows exactly how far or how deep the Duat extends, or if it is even one massive cave system at all. Stories dating as far back as the Age of Darkness tell of adventurers becoming lost for years in its dark passages, emerging hundreds of miles from where they entered. One famous and more recent account has a man traveling over 11,000 miles.
Age of Darkness
There are no confirmed accounts of the Duat during the Age of Darkness; only wild and unconfirmed stories of horrid monsters and massive deep caverns. The only consistent fact of the old legends holds that the Duat is a massive interconnected system, though no formal explorations were ever made. Only the stories of adventurers traveling hundreds of miles underground lend any credence to the tales.
The oldest story comes from the oral tradition of peoples who lived in the Lowland Plains region. The story was first formally recorded during the First Chaotic Period, and tells of a young boy who disappeared into a local cave. Many details were added over the centuries, but the basic tale is as follows: While exploring, the youth became lost. The entire town (or at least a large portion of it) spent weeks searching but never found any trace of him. His family believed he had fallen to his death, or become lost and died of thirst. Ten years passed, and he re-emerged as a grown man. The boy had lost all ability to speak, and looked pale and terrified. Gradually, he relearned to communicate, and told a tale of surviving, alone, eating plants and fish deep in the caves, and searching for a way home. He said that some parts of the cave were dry, empty, and lifeless, while others were full of fresh water, glowing plants, and fish and insects. Entire ecosystems, deep underground.
The story is generally set "a thousand years before High Tower", but historians set the date around 4200 B.G.A. The same tale repeats itself at various points throughout history. The generally confirmed account of Jake Omaze lends signficant credence to the account as Jake's story would seem to indicate that even a young boy can survive in the Duat.
The earliest confirmed accounts of the Duat come from necromanic scribes writing very early in the Mage Wars. The Necromancers were among the first deep miners of the continent, and often spoke of artificial caverns in their writings. They were also the first to use the Duat, as the underground environment was ideal for housing undead.
The Necromancers built colonies and eventually entire cities miles underground, where they found and mined rich deposits of iron, silver, gold, and other metals. By the end of the Golden Age of Necromancy, these underground operations had been abandoned, and by the Dynastic Period their locations forgotten. The Necromancers often left behind undead and ritual sites at these locations, where the dry air could preserve the undead almost indefinitely.
During the early Golden Age, the Slayer Dragons sponsored many expeditions into the parts of the Duat surrounding Arindell. Reportedly, these early explorers claimed to have found both natural and artificial caverns.
By Eieber's own order, many caves were modified for defense of the city. Supply caches, workshops, and barracks were all established underground. New tunnels were cut, natural ones expanded, as was required.
As the city grew, drainage, sewage, and underground transit systems were established beneath the surface. All of these system were connected to the old tunnels, making them an extension of the Duat.
Throughout the Ages of the Alliance, the tunnel system continued to be explored and expanded, though not much beyond the foothills of Stormreaver Range. One very secretive route was mapped from Arindell to the Sword Coast.
During the six Ages of the Alliance, six hundred and nineteen major, documented, well-publicized expeditions were made from various points around the Greater Continent (this figure excludes the explorations taking place out of Arindell, which were focused primarily on defense of the city).
Of those 619, 571 were never seen or heard from again. These expeditions ranged in size from a small handful of men to massive siege-style parties consisting of several hundred explorers.
The largest (and, honestly, most successful) of expeditions was the one led by Jacobi Henry in the early Second Age. This expedition is frequently confused with the far less successful Jacopo Expedition, which happened around the same time.
Jake Omaze gained considerable notoriety in the Fifth Age. As a young boy of fifteen, he left on what he planned to make a three-day expedition into the Duat. He became lost, and was trapped for thirty-one years, emerging over eleven thousand miles away.
Lionel McFerro was a Slayer Dragon during the lage Fifth Age who made numerous trips into the Duat. He is the only person since the early Golden Age to travel the secret routs mapped out by the early Slayer Dragons as escape routes from the city. He later befriended Jake Omaze.
(*Note: Most of these entries involve areas where entrances are known to exist, each area might contain several distinct 'entrances').
There is an entrance in Arindell. This is one of a very few mapped and traversed routes. A well-established path leads from the Arindell entrance to a secret exit near Border Watch and eventually the Sword Coast. Arindell's network of artificial subterranean structure link to the duat in countless places.
There is one in in the extreme south-eastern end of the Agras Plains. This one is particularly curious as it takes the form of a deeply-plunging, apparently natural rock shaft. It has been used only twice; once by Jake Omaze to escape the Duat, and again by a team of spelunkers seeking to verify parts of his story.
There are (or at one time were) dozens of entrances scattered around Arcol Steppe. It is believed the Necromancers sealed many of these.
There is an entrance in Sindall in the Forbidden City.
Rowen has its own network of artifical inter-connected underground structures structures that connect with the Duat.
Ozork Flight has an entrance beneath its eerie, as do many dragon eeries. Some flights even build their eeries within the Duat.
Society of Assassins
The Society of Assassins has an apparently self-sustaining city beneath Ozork Eerie in the Duat.
The Necromancers built at least five large cities (populations over 1 million) deep in the Duat, some as far as nine miles underground. These cities were not self-sufficient and relied on food brought down from the surface. They were mostly mining operations or staging areas for same, and when the mines eventually ran out, the cities were de-populated.
It is also know that the Necromancers built several large monuments and massive tombs in the deep places. In one instance, an entire artificial mountain was supposedly constructed on the surface to seal in a necromancer of such great power, he had nearly ascended to godhood.
The only known contact between the Duani and the surface dwellers comes from Jake Omaze, who recounted meeting them and living among them for several years. Some scholars have claimed his tale is a fabrication, but he was able to recall a considerable amount of their spoken language. Linguists have studied what he recounted, and declared it to be genuine. Since Jake did not have the education required to invent a language on his own, it is generally agreed that his account of the Duani is true.
The Duani most likely entered the Duat somewhere around the end of the Mage Wars. Their oral tradition told that they were driven there by enemies. The Duani do not believe in the existence of the surface, claiming the caves they occupy are in a "magic"level: if one climbs too high, the caves become dry. Too low and they become flooded. The surface is not acknowledged.