There are three primary planes of existence for the Northron tribes:
These planes exist as part of the roots of the World Tree. The World Tree is eternal and exists outside the planes of existence and is also part of them all. Aesenjeim lies near the base of the tree, while Nifenjeim lies far below at its deepest roots. Middenjeim lies in the roots between the two.
This is the mortal realm of Northron cosmology. It is also home to the elemental lords. Essentially, Middenjeim encompasses the Material Plane, the Ethereal Plane, the Plane of Air, the Plane of Fire, the Plane of Earth, the Plane of Water, the Negative Energy Plane, and the Positive Energy Plane.
Home of the gods, Aesenjeim is also the closest plane to the branches of the World Tree. It is home to several important sub-realms (or “halls”). It is one of the Outer Planes.
Valhalla is home to those slain in battle. Here the fallen gather to celebrate their victories and train to fight in the final battle against the Grundr.
The hall of the All-Father, Yülthn, contains his High Seat, from which he can see anywhere in the three planes.
This is a communal hall used by the gods to assemble to discuss events and decide important issues.
Each of the gods have their own hall. The aspects of that hall often reflect its owner in some way. Seldom are mortals allowed in such sanctums.
Nifenjeim is the lowest of the three realms, the realm of the goddess Eydis. It is the underworld to which the dead who have not fallen in battle go. Here they must appease the goddess or live in an eternity of torment. It is one of the Outer Planes.
Between the three realms, and straddling them, is the Gate. It is the passage through which the gods pass to gain admittance to each realm. It is guarded by Saemundil, the guardian god.
The true nature of The Gate is a mystery. Some metaphysical scholars believe that it is a demiplane that allows for quick travel through the Astral Plane between the Material Plane, Aesenjeim, and Nifenheim. This would account for its existence in the current planar models. The myth of the World Tree is usually counted by Midron and Southron scholars to be just that, a myth concocted by their Northron neighbors to explain the existence of the planes.