The Far Realm, also called Outside, is a plane—or perhaps a space beyond the planes—that is terrifyingly remote from standard planar geometry. The creatures that abide in the Far Realm are too alien for a normal mind to accept without being damaged. Where stray emanations from the Far Realm leak onto the world, matter stirs at the beckoning of inexplicable urges, then burns to ash or takes on monstrous new life.
Thankfully, this realm of madness only rarely touches the rational world. The Far Realm is not normally a place one can visit, and its terrible, insane influences are infrequent in the world. When these rare intrusions occur, the warping pressure of the Far Realm transmutes previously inert substances. This blending of realities results in horrifying corruptions, disruptions, and sometimes even the birth of squiggling aberrant monstrosities.