These facilities float high above the ground to keep them safe from the majority of Flood if there is ever another major outbreak on the Installation. During Halo 2, they first appear in the level Sacred Icon when the Arbiter reaches the inner abode of the Sentinel Wall. In the next level, players are able to observe the same crashed structure being damaged by Wraiths and Scorpion tanks and fight through it as Sentinels and the Flood fight each other.