The 'Weir Gate' leads, or will lead, to the Slipstream Realm where you mortals have or will establish your Battlespire Academy. Regarding the 'Slipstream' designation: mortals, of course, can only perceive Oblivion and the astronomical regions of the Mundus in terms of their own frames of reference. They 'see' only what they can comprehend, and often that isn't much. Furthermore, what they do comprehend often seems to drive them insane, though the rate of mental deterioration varies with individuals. Twice upon a time, the Imperial Mananauts regularly ventured beyond Nirn, and in doing so learned that the mortal mind is best acclimated to other realities by gentle degrees. This is one of the reasons why Maelstrom seems to resemble aspects of your world—I wished it to be mortal-friendly, or at least friendly enough for mortals to experience my arenas without distorting their mentalities! Anyway, the Mananauts will learn that it's best to train for Oblivion in a transition zone, a place where differing truths can co-exist without conceptual abrasion. At certain points, transliminal forces balance in standing waves, and these regions are designated 'Slipstream Realms.'

Visits to Aetherius occur even less frequently than to Oblivion, for the void is a long expanse and only the stars offer portal for aetherial travel, or the judicious use of magic. The expeditions of the Reman Dynasty and the Sun Birds of Alinor are the most famous attempts in our histories, and it is a cosmic irony that both of them were eventually dissolved for the same reason: the untenable expenditures required to reach magic by magicka. Their only legacy is the Royal Imperial Mananauts of the Elder Council and the great Orrery at Firsthold, whose spheres are made up of genuine celestial mineral gathered by travelers during the Merethic Era.

Well, certainly, in his youth it’s well known that the esteemed Abnur Tharn, Chancellor of the Elder Council, received training as an Imperial battlemage from whatever tradition remains in the Imperial City since the fall of the Potentates. And there may be other holdovers from the glories of the Second Empire, from groups such as the Dragon Guard or the aforementioned Shadow Legion or even the mysterious Imperial Mananauts, maintaining and passing on their traditions through new names and guises. But my guess is they’re all keeping their heads down until we see a conclusion to this ruinous and destructive Alliance War.