Abyss

One of the more infamous Elsewhere, being the target of many expeditions and a place of bountiful riches awaiting those that manage to retreat from it with their sanity and corporeal stability more or less intact. It's also rather hard to actually reach, with most of the located entrances being kept secret by organizations that located them. As a result, a big part of public knowledge about it is hearsay at best.

Geography

Abyss is a multilayered space of undetermined size, with the full number of layers being similarly undetermined. Each layer has its own unique biome and theme, its own ecosystem (or lack of it) and is home to a variety of supernatural entities. By general rule, the deeper you go, the less the layers resemble something that could be found in the real world, with more and more dangerous entities to be encountered there.
There are places where one can head up and down, often rather hard to find. As a result, maps of scouted Abyss layers are among the most valuable things in the Abyss. Due to the fact that retreating from deeper layers requires you to go all the way back on foot, you can expect most organizations that attempt to explore it to have a network of outposts scattered around. And even there, while taking the shortest route, you can expect the walk back from the deeper layers to take months, all while being deep into one of the most hostile environments ever.
There is a theory concerning its existence, one that is generally considered to be rather worrying. According to it, Abyss was never supposed to be walked down from Earth - it was instead created as a sort of an existential stairwell allowing other things to walk up towards Earth, with a lot of greater aberrants and gods (especially Disasters) that appear out of nowhere on Earth coming out of the Abyss. With them simply taking a shortcut out of it instead of trying to barge through human-held exits.
Example layers of the Abyss:
Layer Four: The Frozen Waste - A completely frozen, boreal landscape full of glaciers and with an eternal snowstorm raging all throughout it, with an estimated size of Australia. Some claim that there is a cold ones community supposedly worshipping one or more Embodiments of Ice hidden somewhere out there, but all supposed evidence for that is rather sketchy at best.
Layer Fifty-Eight: The Void of Existence - The deepest layer of Abyss that was reached thus far, with no subsequent attempts to return there. The recordings of it display a three-dimensional void with starlight sky as the background in all direction, with a network of stairs and platforms scattered all throughout, connected into one complicated network. It's also basically filled with high category greater aberrants.

Natural Resources

Aside from first two or three layers, Abyss is way too dangerous for any mining or agriculture operations, aside from whatever minimal things are required to keep an outpost in a working order while getting supply runs from the base camp outside of Abyss once every six months (and that's if you're lucky). What is obtained from the Abyss is instead loot from slain supernatural entities... and scavenging.
It's uncommon to, if you have a good luck, run into a corpse of freshly slain greater aberrant or a god that came into blows with something else and died. It's not uncommon to run into artifacts just lying around, waiting to be picked. Sure, it's not common, but each time it happens, it will pay back the costs of running an outpost in the Abyss.

Statistics

Summary

Size: Undetermined
Danger Level: Varied
Usefulness: Varied
Accessibility: 2/5

Danger Details

SHALLOW ABYSS [Layers 1-10]

Lesser Aberrant Presence: 1/5
Greater Aberrant Presence: 1/5
Gods Presence: 1/5
Demihuman Presence: 0-2/5
Undead Presence: 0-2/5
Cryptid Presence: 0-2/5
Other Threats: None

UPPER ABYSS [Layers 11-23]

Lesser Aberrant Presence: 2/5
Greater Aberrant Presence: 3/5
Gods Presence: 2/5
Demihuman Presence: 0/5
Undead Presence: 1-3/5
Cryptid Presence: 1-3/5
Other Threats: None

LOWER ABYSS [Layers 24-42]

Lesser Aberrant Presence: 3/5
Greater Aberrant Presence: 4/5
Gods Presence: 3/5
Demihuman Presence: 0/5
Undead Presence: 2-4/5
Cryptid Presence: 2-4/5
Other Threats: None

DEEP ABYSS [Layers 43-58]

Lesser Aberrant Presence: 4/5
Greater Aberrant Presence: 5/5
Gods Presence: 3/5
Demihuman Presence: 0/5
Undead Presence: 0/5
Cryptid Presence: 0/5
Other Threats: None

Usefulness Details

Agriculture: 1/5
Mining: 1-2/5
Hunting: 5/5
Others: None