The Hypokeimenon (Labyrinth)

As little as is known of the the Noumenon, even less is known of the Hypokeimenon, so much so that most dismiss it as speculation and rumour. The only sources only vaguely refer to another purpose to the Labyrinth, not another installation, and the word itself, Hypokeimenon, is just the translated Sangheili name given to a hypothetical installation. No sources actually name it, or specify its true purpose.
Engagements against Sov-
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>ALERT: Incoming transmission:
>Unksdr: You pretend your affairs matter. That the galaxy cares about your petty wars and mere trillions dead. You worship those who are now but dust and are no longer there to be offended by your arrogance.
>Unksdr: Children. You’re all just children.
>Unksdr: Delicate. Fragile. Immature.
>Unksdr: And all the more dangerous for it.
>Unksdr: Our Mantle was passed on to ensure that we rose above such pettiness. It was ignored and forgotten, reduced to folklore and myth. And now you pay the price for such abuse of power. We watched as they squandered the sacred charge given them, and we watched as they sowed the seeds of their own destruction.
>Unksdr: It was a bitter harvest.
>Unksdr: We watched as they did what had to be done, finally understanding their charge; guardians of life, eternal sentinels safeguarding the galaxy. They fulfil their duty better in death than they did in life.
>Unksdr: But they overstepped their boundaries.
>Unksdr: The Mantle they were given was not theirs to pass on. Their inheritors have been left an “empire” they have not earned. 
>Unksdr: We cannot allow that.
>Transmission interrupted - unable to reestablish contact