The Paludarium

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. Ancient elves once opened a vast portal to the Far Realm within a mountain called Firestorm Peak, but their civilization imploded in bloody terror and the portal’s location — even its home world — is long forgotten. Lost portals might still exist, marked by an alien magic that mutates the area around them.

Geography

The Paludarium, also known as The Infinite Library, is a plain of existence containing endless halls filled with books. Appropriately called The Paludarium, this plane's terrain varies from stuffy halls filled with expertly crafted bookcases reaching the ceiling to vast forests with flowing rivers where the trees themselves serve as bookcases.

Ecosystem

The plane itself serves as an example of a perfectly balanced ecosystem. Trees are transformed into books and as life in the library grows its magic is transferred back into life.

History

The Paludarium and Mimir share the same life essence. Both were created at the same time and shall disappear together as well. The Paludarium is the paper which Mimir fills with the universe's knowledge.
How exactly Mimir and The Paludarium came into existence is unknown. Many have speculated their collaboration to be the fast-expanding universe's need to keep up with itself, others consider their presence is merely here to serve as inspiration for the great writers.

Tourism

Mimir and The Paludarium live happily together in seclusion. The plane itself is rarely visited, for not many know (or believe) in its actual existense. Those few who have found their way to its borders have turned to madness at the abundance of knowledge.