The Realm of Wizards is another dimension.
higher plane accessed through the Wizard's Institute of Technocery. The realm is above the mere mortal plane. One may enter the Realm of Wizards after finishing the initital test to become a Wizard Initiate.
It appears that Wizards are able to properly ascend to a higher state of being and gain immortality. The Realm of Wizards is one of these places where they granted immortality.