The Abyss

"The allure of the abyss is inescapable. Even so, no one has managed to reach the end. A golden city that sleeps at the bottom of the abyss. Relics that surpass understanding. For 1900 years we have ventured into the darkness hoping to make greater and greater discoveries. The romance of a lost age and the arcane. Drawn to the great unknown, the abyss devours us."

About
The Abyss is a colossal pit discovered 1900 years ago around the islands of the southern ocean of Beolusk. The vertical hole has a diameter of around 1000 meters and it's at least 20,000 meters deep, with its exact depth being currently unknown. It possesses a unique ecosystem, wherein lie the remnants of an ancient, yet advanced civilization that made their home there in the distant past. Hiding countless treasures and relics of immense value inside, many explorers have challenged the mysterious Abyss. Some are treasure hunters looking for the Artifacts inside, and others are explorers determined to unveil the secrets it hides. In order to explore the Abyss, valiant cave raiders called Delvers were born, and the town of Orth was established at the edge of the abyss.

Even after so many years, the Abyss still contains many sections that have never been seen, as the hole carries many dangers. A hazardous habitat that defies common sense and other-worldly creatures that have adapted to its unique environment are some major obstacles that face explorers of the Abyss.

All over the Abyss there is a mysterious force field called the 'Lifeblood of the Abyss'. The force field acts as its main source of energy, carrying nutrients, producing light and sustaining life, in a similar fashion to the Sun. While it is present everywhere, it seems to be more prominent the closer one gets to the center. More savage and dangerous creatures are often found in areas where the force field is most prevalent and the branches of the vegetation always point towards the center of the hole, their main source of energy for undergoing photosynthesis. Delvers use this fact to guide themselves when they are lost. The force field itself is invisible to the naked eye, but it can be detected as a vague fog that limits vision for humans. The field is also constantly moving, following the consciousness of living beings. There are a few selected spots in the Abyss, usually far away from the center and in secluded areas, where the force field doesn't exist or is extremely weak.

The great pit also appears to have some form of time distortion, though it is unclear if this is a fact or merely a feeling. The White Whistle Ozen claims that the deeper one delves, the more your sense of time breaks, with the effect becoming extreme from the 5th Layer onwards. As an experiment she once descended what she thought were a couple of weeks, but by the time she returned to the surface several months had passed. While there's little evidence to prove it, she considers it a possibility that time speeds up the more one descends.

The Curse of the Abyss
Though the Abyss is riddled with countless dangers and hazards, one of the greatest challenges facing delvers is, in fact, the ascent from it.This is due to a phenomenon called the Curse of the Abyss. The term refers to a series of symptoms that manifest upon ascending while inside the abyss, with its more scientific name being "Strains of Ascension". The effects of the curse manifest after ascending around 10 meters within the Abyss, and there's no way to avoid it through conventional means. For some reason, the Curse only affects humans and Narehate.

The deeper one delves, the more severe the symptoms are, ranging from dizziness and nausea to intense pain throughout the body, loss of senses and even death. This makes the return trip from the Abyss extremely difficult, and it is not uncommon for delvers to perish on the way up. Particularly, the curse of the 6th Layer("loss of humanity or death") makes the return journey physically impossible for humans.

The curse results from piercing the force field of the Abyss while ascending, although this fact is not generally known. Therefore, areas where the force field is weaker also result in the effects of the curse being less severe. In certain specific places, like Nanachi's Hideout, the force field isn't present at all, and so the Curse doesn't occur either.

The Blessing of the Abyss
An exceedingly rare and top secret phenomenon occasionally takes place within the Abyss under very specific circumstances. It was first discovered by the White Whistle Bondrewd when he was experimenting with the Curse of the 6th Layer. Much like with the Curse of the Abyss, the event occurs during the ascent, but two people are needed to witness the phenomenon. By having one carry all the burden of the curse onto himself (through the use of an artifact or another similar instrument) the other will be able to avoid the curse entirely. Through modifying several artifacts, Bondrewd utilized an elevator with two capsules that separate the curse and force it onto one of the two. Usually, if the one receiving the curse doesn't die midway through, this merely results in one of the two being spared the effects of the curse. However, during a certain experiment he discovered that a strong relationship of deep love between the two results in the event he called a "blessing" for the one that wasn't receiving the burden of the curse. While he couldn't explain the reason for this, it was factually proven.

The appearance of the blessed changes, growing fur all over the body and mutating some of his traits like the eyes or fingers. The blessing is not merely in looks however. The one gifted earns the ability to observe the force field of the Abyss, something that only the predators of the deep are able to see, and is an incredibly useful ability for delving in the pit. It also appears to increase their physical fortitude to some extent.

Abyss Faith
A religion that was formed using the Abyss itself, and it appears to be a very common belief for those that delve into the Abyss. Instead of believing in a God, those that turn to this religion believe in the Abyss itself. Because the bottom is unknown, it replaces their God and grants them hope in the after-life. It's based on the principle that if you lose your life within the Abyss, your soul will descend to the bottom and live as a form of spirit of the abyss. The unreachable depths of the pit makes people believe that it transcends life itself.

1st Layer: Edge of the Abyss

 * Depth: 0~1350 meters.


 * Strains of Ascent: Light Dizziness and Nausea

The first layer is the most shallow section of the abyss, right below the Town of Ooth. A gondola was built between 50 and 580 meters to hasten the descent. The environment doesn't really change and wildlife consists of mostly harmless animals, though occasionally predators from the 2nd Layer might ascend in search of food. There aren't many treasures or relics either, but there is a considerable number of Praying Skeletons.
 * Description: 

2nd Layer: Forest of Temptation

 * Depth: 1350~2600 meters.


 * Strains of Ascent: Heavy nausea, headache and numbness of limbs.

The Forest of Temptation is the first truly dangerous section of the abyss. The fauna and environment suddenly change, turning into a tropical rainforest with huge vegetation. It is filled with dangerous beasts and ascending becomes increasingly difficult, making it a place where only experienced explorers can delve into. If a red whistle delver somehow gets to the 2nd Layer, search parties are called off and it is treated as a suicide.
 * Description: 

On the deepest point from 2000 meters onwards, the habitat suddenly flips around and becomes the "Inverted Forest". Predators in the air become common and wind currents are very strong and unstable. It also gets colder and darker since it receives little light due to its inverted position. At the farthest from the center an Observation Camp was built to serve as a resting point for delvers. Currently the white whistle Ozen is using it as her base.

3rd Layer: Great Fault

 * Depth: 2600~7000 meters.


 * Strains of Ascent: Vertigo combined with visual and auditory hallucinations.

The third layer consists only of a 4000 meters vertical cliff, making it a highly challenging area to cross. Countless methods have been attempted to cross it through the use of artifacts or differently crafted devices. Aerial predators are common, including Scarlet Maws.
 * Description: 

4th Layer: The Cup of Giants

 * Depth: 7000~12000 meters.


 * Strains of Ascent: Intense Full-body pain and hemorrhage from every single orifice of the body.

The 4th layer is the point where the curse of the abyss gets truly severe and could potentially kill a person if it's someone already wounded or weak. It is invaded by some absurdly overgrown vegetation, with 800-meter-tall plants shaped like cups. Plants have extremely fast growing rates on the 4th layer, making the layout of the place constantly changing. Because of this, it is impossible to make maps or a chart. The fully grown cups are filled with hot water in the top, but the ones that are not fully grown produce acid instead. The most dangerous beast is the Tamaugachi. While it is herbivorous it is highly defensive of what it considers its territory, and will attack anyone it sees nearby.
 * Description: 

In the middle region at the 9000 meters marks there is the famous Garden of the Flower of Resilience, an area filled with Eternal Fortunes, the trademark flower of the Abyss. The distinctive sight produced by the countless glowing flowers make of the garden one of the most beautiful landscapes of the Abyss.

5th Layer: Sea of Corpses

 * Depth: 12000~13000 meters.


 * Strains of Ascent: Complete sensory deprivation, confusion and self-harming behavior.

The 5th layer is the world that only white whistles delve into, and according to Shiggy you can count the number of people who successfully returned alive from here with the fingers of your hands. It is the thinnest layer of the Abyss vertically, being only 1000 meters deep, but it is also the widest one horizontally, probably around 10 times wider than the town of Orth. It consists mostly of a large sea with some crystallized sections, and the water is being held up by a large layer of thick muddy water. The water is filled with monsters of the sea, and diving deep into the water is synonymous with suicide, since swimming back up would make someone be hit by the curse of the abyss. Because it is the last section of the abyss where it is physically possible to survive a return trip, it is quite common for white whistles to set down here for some time.
 * Description: 

At the deepest point, a fort was established by the white whistle Bondrewd, named Idofront. Because it is just above the 6th layer, a device akin to an elevator exists right on its center. Normally, descending from the 5th layer would require to dive into water and swim, but this nearly impossible to achieve, so the device is required to descend. However, it can only be activated by a white whistle, or more specifically, by a Life Reverberating Stone, the material white whistles are made of. However, since their whistles are especially designed so that they can only be used by their original owners, the altar is only available to them.

6th Layer: The Capital of the Unreturned

 * Depth: 13000~15500 meters.


 * Strains of Ascent: Devastating body alterations that result in the loss of humanity and sometimes death.

The 6th layer is the point of no return, since it becomes humanly impossible to survive the ascent. When a white whistle delver descends to the 6th layer it is called "The Last Dive".
 * Description: 

In the Capital of the Unreturned, the ruins of a majestic city sleep undisturbed. A rumor in Orth exists about a Golden City sleeping at the bottom, which originated from this very city within the 6th Layer. Creatures of Irrational danger level like the Kuongatari become quite common.

The Curse that manifests upon ascending within the 6th Layer subjects the victim to an inconceivable pain and leads him to mutate into a messy pile of meat. Humans sometimes survive the effects of the curse, but their intelligence and consciousness vanishes, devolving into something mindless that acts purely on basic instincts like an animal. These creatures have been named Narehate by delvers, and if encountered they're usually killed in order to release them from their form. As it turns out, the form a human takes when becoming a Narehate seems to be closely related to their desires and dreams. In a secluded area of the 6th Layer, an entire Village inhabited by Narehate called Ilblu was formed.

7th Layer: The Final Maelstrom

 * Depth: 15500~????? meters.


 * Strains of Ascent: Certain death.

The final layer of the Abyss. Not much is known about it but there are many rumors about it. Some white whistles have claimed that from above it can be seen something shaped as a ring.
 * Description: 

The Deepest Point

 * Depth: >20000 meters.


 * Strains of Ascent: ????


 * Description: No-one has reached the deepest point but it's been confirmed that it's beyond 20000 meters deep.

Trivia

 * The Abyss is sometimes referred to as "The Netherworld".
 * The map of the abyss was the first concept of the series drawn by Tsukushi, and he was inspired by roleplaying games like Wizardry that he used to play as a kid.