Far Realms

An utter alien realm beyond the scope of anything conceivable by the known realms of psychics and time. Those who have witnessed or conceptualized this place have only seen the tip of the iceberg and even doing that almost always drives them mad.

The Far Realms are home to the Elder Evils 

From DMG:

The Far Realm is outside 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. Aberrations such as mind flayers and beholders are either from this plane or shaped by its strange influence.
The entities that abide in the Far Realm itself 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. 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 Realm has no well-known portals, or at least none that are still viable. Lost portals might still exist, marked by an alien magic that mutates the area around them.

Type

Dimensional plane