Manual of Elsewheres
Elsewheres is a joint term for all places that aren't part of the Physical Realm (known also as Material Reality, Reality or Real World). Attempting to describe them all is a complicated matter due to their chaotic and often hard to comprehend nature. Guesswork and increasingly incoherent sentences tend to result from such endeavours. While there are several major Elsewheres that are commonly known throughout the world, there are also many that are much harder to access. The level of knowledge about them varies between the various communities, and it's not unheard of for a coordinates and an access method to a useful Elsewhere to be one of the most valuable and strictly guarded secrets of some magical organization. Due to how unique most Elsewheres are (starting at environment and ending at geometry), it's nearly impossible to explain them as a group. Even the name itself implies that, Elsewhere being any place that isn't 'here'. Expect very little answers, a lot of weird landscapes, lifeforms that shouldn't exist, and wonderful treasures to be uncovered - although typically guarded by things that barely register humans as potential threats.
Elsewheres are varied. Some of them appear to have relatively Earth-like geography, with mountains, trees and so on. Even those Elsewheres are typically wrong on some deeper, less-noticeable level. Most of such places are also speculated to have been at some point part of Earth, explaining their relative similarity to Earth (or, at the very least, the Material Reality that it represents). Others are much more alien. Impossible landscapes (how about having another surface instead of the sky), impossible materials (think lakes of human spinal fluid that also rains from the skies), and often impossible logic. Such as going around a tree (or tree-equivalent) making you appear at a different location depending on which side of the tree you took. Or towers that you climb only to emerge in a completely different place... but on the ground level. Attempting to make sense of the geography of the Elsewheres tends to be confusing.
There are many materials within the Elsewheres that cannot be obtained on Material Realm. However, they all carry the taint of the Elsewheres. Expect them to be fully covered by the Censor's Veil, and prolonged interaction being dangerous to humans. Organized resource correction is possible in some Elsewheres. It depends entirely on the threat level of the Elsewhere in question, and whether the resources present them warrant dealing with a threat of this magnitude. When that isn't the case, you can expect materials to be produced in an extremely short supply.