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. The Curse affects all living things, however the creatures that inhabit the abyss have developed ways to sense its flow and avoid it.

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 and The Village of Ilblu, the force field isn't present at all, and so the Curse doesn't occur either.

Rare Phenomenon

 * Birthday-Death Disease - a strange disease that occurs on the surface, caused by an abyss' curse. A lot of people died at the same day of the year they were born, has been called off as a "rumor" but in entirety it becomes true. Its symptoms usually starts with a high fever and forcibly becomes an unknown condition that cannot be treated by ordinary doctors. The victims of the disease still counting in Orth.

However, there is evidence pointing to the force field as a possible cause of this illness, as it's revealed that once one is removed from Orth, the sickness vanishes, as if it were never present at all. At the current time, Kiyui is shown to be the only survivor thus far.

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 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 Orth. The environment doesn't really change and wildlife consists of mostly harmless animals.
 * Description: 

2nd Layer: Forest of Temptation

 * Depth: 1351~2600 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. The creatures that inhabit this layer are much more dangerous. Deeper in, there is an area known as the "Inverted Forest," where the trees grow upside-down. Here an Observation Camp was once built to serve as a resting point for delvers.
 * Description: 

3rd Layer: Great Fault

 * Depth: 2601~7000 meters.


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

The third layer consists of a 4 km vertical cliff, making it a highly challenging area to cross, save for the large cave network around the main shaft. Countless methods have been implemented by many in order to attempt a descent, to varying effects. Aerial predators are common, including Scarlet Maws.
 * Description: 

4th Layer: The Goblet of Giants

 * Depth: 7001~12000 meters.


 * Strains of Ascent: Intense Full-body pain, dizziness from pain and varying amounts of internal and external bleeding across the body.

A strange, humid jungle of strong vines weaving to form giant concave discs that capture water from the air earn the 4th layer its name, the "Goblet of Giants." At 9000 meters marks the famous Garden of the Flower of Resilience, an area filled with Eternal Fortunes, the trademark flower of the Abyss. A truly beautiful sight, though the danger from the beasts that dwell here is high.
 * Description: 

5th Layer: Sea of Corpses

 * Depth: 12001~13000 meters.


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

The thinnest layer of the Abyss vertically, being only 1000 meters deep, but the widest one horizontally, probably around 10 times wider than the town of Orth. It consists mostly of a large, monster-filled sea with some crystallized sections, held up by a thick layer of dense mud. This is the last layer of the abyss where it is possible to bear the curse and return alive and intact. And ancient ritual site, Idofront, acts as a gateway into the 6th layer, the point of no return.
 * Description: 

6th Layer: The Capital of the Unreturned

 * Depth: 13001~15500 meters.


 * Strains of Ascent: Loss of humanity or death, or very rarely, the Blessing.

A White Whistle's last dive. A human who tries to ascend from the 6th layer either succumbs to death, or is deformed beyond recognition, hence the name, "The Capital of the Unreturned." In Orth, there is a rumor about a Golden City at the bottom of the abyss, which originated from the 6th layer, where the ruins of a majestic city sleep undisturbed. It is not uncommon to come across creatures of an Irrational danger level here. In a secluded area of the 6th Layer, an entire Village inhabited by nnarehate called Ilblu was formed.
 * Description: 

7th Layer: The Final Maelstrom

 * Depth: 15501~????? meters.


 * Strains of Ascent: Certain death.

The final known 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 role-playing games like Wizardry that he used to play as a kid.