Threshold

Threshold is a complicated and rather unique case of an Elsewhere with an undetermined size and that is only barely explored by now. It's considered to be one of the less dangerous Elsewheres (where the worst threat, typically, is the risk of getting lost in the maze).
As a result, while it's rare, there are cases of roads being charted through Threshold. This is actually a problem due to usefulness in smuggling things.

Geography

Threshold is best described with the word 'liminality'. A single expedition to Threshold could provide one with literally any idea of pictures associated with that concept. It's an endless maze of undetermined size, with rooms, corridors, hallways and a handful of very limited open spaces. All of them are best described as 'wrong'. Most of it is somehow incorrect.
The random furniture scattered all around is just not right, the shapes of the room is just not right, literally everything is just not right. It's unnerving. This place due to its completely nonsensical outline is very easy to get lost in.

Natural Resources

There isn't a lot of natural resources here, if only due to the fundamentally urban nature of the environment. There is no ground and ore to mine, there are no rocks to dig out in a quarry, there is no ecosystem to produce alchemical components.
The only resources to obtain from here are either construction materials or things taken from killed entities that sometimes frequent this location.
There were cases of connection being established between the Threshold and other Elsewheres to allow for easy transit of said construction materials, that are available in Threshold in literally any amount and for the cost of work needed to disassemble the walls and floors. This, however, is a rather rare case.

History

Threshold is a relatively new addition to the world at large, with the first confirmed entrance to it in 1992. This is a confusing thing to magical community at large, due to Threshold now being available from most parts of the world.
This isn't a normal mechanism for most of the Elsewheres. As a result, this particular world is a subject for many theories.
The one that is most likely to be correct (while also being practically unknown to the world at large) is Threshold being created as a result of someone attempting to (somehow) draw an Isolation Glyph on a concept of liminality, perhaps as an attempt to curb influence of a Power connected to it (perhaps the Ancient of Reflections).
Its return to the world would thus be the result of the can leaking. There is no conclusive proof for that, nor are there any theories on how such an achievement was possible.

Statistics

Summary

Size: Undetermined
Danger Level: 1/5
Usefulness: 1/5
Accessibility: 4/5

Danger Details

Lesser Aberrant Presence: 1-2/5
Greater Aberrant Presence: 1-2/5
Gods Presence: 1-2/5
Demihuman Presence: 0/5
Undead Presence: 0/5
Cryptid Presence: 0/5
Other Threats: 0/5

Usefulness Details

Agriculture: 0/5
Mining: 0/5
Hunting: 0/5
Others: Building Materials