Mahnuj is the plane or realm of existence that encompasses Kalgranoon, its moons, and Ursia, the Sun. Mahnuj is believed to not include Karkien, as it is believed to be its separate realm entirely. Mahnuj is believed to refer to the above mentioned things alone. Mahnuj was a construct created by Lilyath and the other gods, as such, many believe that the remaining gods exist somewhere in Mahnuj.
Mahnuj was believed to be conceived from the Void by Lilyath. And was considered to be one of the very first realms created. After the creation of Mahnuj it is said that Lilyath then created Kalgranoon, and afterwards, it's moons. Once Lilyath had created Kalgranoon she became tired and returned to Aalguden. Her sudden return to Aalguden created a disturbance in Mahnuj, which resulted in the creation of the Sun and stars.
Due to this, mages tend to regard the stars, sun, and moon as sources of power. It is because of this that the stereotype of an old wizard wearing a robe filled with stars and moons was created.
At the end of the Second Era, the Three Travelers left Mahnuj agreeing that the fate of Kalgranoon was of greater importance than the damage that their leaving Mahnuj might cause. They passed through the inter-planar vale into Karkien, the realm of Asurmen and his underlings in order to seal the realms from each-other once and for all. This passage out of Mahnuj caused a disturbance just as Lilyath's did at the dawn of time. A crack was created the the very fabric of the realm, causing a major leak of arcane energies into the void. When the gods sealed themselves from Mahnuj, the sources of the magic were extinguished, and it began fading slowly but steadily. Some scholars of divination have suggested that the gods have not returned to Mahnuj because they are attempting to seal the leak that they have created from the outside, but nobody knows in certainty.