Core room antechamber

The Core Room Antechamber was a massive chamber located at the center of Onyx. The Antechamber served as the only entrance to Shield World. Upon the powering up of the Halos, the Antechamber would become accessible by teleporter connecting to installations closer to the surface of Onyx.

The actual entrance to Shield World was itself in the center of a large stepped structure within the Antechamber. The structure would gradually 'flatten' until it became level with the ground. At this point, the entrance to the Shield World would be sealed.

The Antechamber was the site of a desperate rearguard action by Spartan-II's and -III's led by Spartan-051 against Covenant forces under Voro 'Mantakree during the Battle of Onyx. The Antechamber was destroyed with FENRIS Nuclear Warheads by Spartan-051, who sacrificed himself to deny the Covenant access to Shield World.