The Unnamed Halo control facility was a control structure, similar to the Ark outside the Milky Way galaxy, used to remotely activate all of the Halo installations at once. It was located in the Mundus Magicus alternate dimension as part of the Forerunner experiment in creating artificial galaxies in parallel dimensions. The facility occupied an areolunarstationary orbit around the outermost moon of Terras Magicus, remaining in such a position that it was never visible from the surface of the planet.
Its existence was a failsafe; if the Milky Way was overrun by the Flood, and the Ark either failed or was similarly compromised, then this facility in the alternate dimension, unreachable by the Flood, would then be used to sterilize the Milky Way galaxy. At the peak of the Forerunners' power, the facility was staffed by an alert crew at all times, monitoring the slispace communications with both the Ark and Forerunner facilities in the Milky Way galaxy, prepared to act as the final solution against the Flood.
Following the collapse of Forerunner society, the facility went dormant for 100,000 years, until discovered and occupied by Kawakami Gensai, who attempted to use it to activate the Halo installations while holding open the gateway between the Old World and the Magic World, thus killing all sentient beings in both dimensions. Following his defeat by the combined forces of Ala Alba and Kuro Arashi, the facility remained in orbit until sometime prior to the Human-Covenant War, where it was destroyed by a volley of MAC rounds from the UNSC Yamato following the ship's design upgrades.