Gargash

Very little is known about the realm of Gargash, save that it was exiled along with its master, Torog, after the War of Creation had ended. Gargash was once a mighty primordial, the bitter enemy of Torog (who, at the time, was among the good-aligned gods). At the moment the War of Creation started, Torog had set out into the deep portions of the earth in search of Gargash, to put an end to his strange and cruel experiments. Though the two did not take part in the War of Creation, they fought a war between themselves, with Torog eventually gaining the upper hand and bringing Gargash to his knees. Before Torog could strike a fatal blow, however, Gargash cursed him to never heal from his wounds, and never be able to leave the deep places of the earth again. And though Torog slew Gargash, and tried for many eons to return to the surface, dragging his broken and bleeding body through the earth, carving out what would eventually become known as the Underdark, he found that he could not do so.
And so, mind broken by the years of pain and torment, Torog settled into madness among the corpse of his old enemy Gargash, carving out a domain in the remains of the great primordial. It was here the Benevolents found him, and, seeing the madness he had descended into, banished him to the Far Realm, along with his domain of Gargash.

Geography

Next to nothing is known about the current geography of Gargash. Prior to its exile, it was formed from the remains of a great earth primordial, and as such, consisted of large formations of rock and earth, in which Torog had made his citadel. It's current state in the Far Realm, however, is beyond the estimation of even the world's greatest scholars.