Far Realms

The Far Realms are planes of madness and horrors where the fundamentals of reality break down. The endless madness of the Far Realms has been known to twist the forms and minds of creatures unfortunate enough to visit the planes. The Far Realms exist beyond the known multiverse. In fact, it might be an entirely separate universe with its own physical and magical laws. Where stray energies from the Far Realm leak onto another plane, matter is warped into alien shapes that defy understandable geometry and biology.
For mortals, knowledge of the Far Realm is a struggle of the mind to overcome the boundaries of matter, space, and sanity. Some warlocks embrace this struggle by forming pacts with entities there. Anyone who has seen the Far Realm mutters about eyes, tentacles. and horror.
The Far Realms seem infinite in size, or at least so large that it makes no difference. Within the Far Realms, landmarks and entities seem to exist in multiple places at the same time. Although full of a dark nothingness, the Far Realms is full of bizarre scenes and what passes for wilderness. Strange blue globes can rain down from unseen heights, bursting when they strike something and unleashing horse-sized ticks that immediately scuttled away to hunt for blood. Gelatinous worms crawled through the Plane. Forests of writhing tentacled vegetation were encrusted with orange moss, growing above an amoebic sea. At the very limit of sight drift huge shapes, vaguely resembling creatures of the deepest ocean, but the smallest being the size of a city, and they seem not to notice the lesser beings.

Portals to the Plane

The Far Realm has no well known permanent portals and spontaneous portals are thankfully rare, but when they do form incursions from alien forces begin.

Denizens of Madness

The entities that abide in the Far Realms themselves are too alien for a normal mind to accept without strain. Titanic creatures swim through nothingness there, and unspeakable things whisper awful truths to those who dare listen. The Far Realms are thought to be the birthplace of the foulest aberrations, including, aboleths, beholders, illithid, and slaads; it is also said that they are home of Elder Evils eldritch horrors who are said to be older than existence and as powerful as deities.