Earth, and the reality it resides in. The normal world is where all realms intersect.
Also known as the 'Land of Dreams and Mist', the Elementalia is a realm of powerful thought, enriched thickly by magic. In the days of old, the ancient people of the westerly nations worshiped the gods of this realm, passing minute amounts of mana into it through their faith. This kept the realm alive, and in return, the gods mad manifest of themselves to fight for and defend their faithful. Old hedge-mages would make gates into this land to practice magic with unlimited abandon, or to find safety against the travails of the world. The Elementalia was a safe haven for those who could use it. Yet, the warring middle ages forced a decline in worship, and the gods that shaped the Land of Dreams and Mist became weak, and so did their world. In response, what little worshipers were left created a staff to maintain their connection with the other realm, but found that all they had done is seal the fate of their gods. Unity became a zip-tie to the income of mana, forcing itself to be the only way the energy could be deposited, making the staff a dangerous vacuum to anyone who touched it. Thus, the world went dark was not heard of again for many, many years.
It is theorized that this realm is the argued birth-place of mana, considered how the energy itself permeates the place.