Sentinel Headquarters was a level cut from Halo 2 due to time constraints. Little is known of it other than that it involved the Forerunner machinery, the Sentinel. The environment was nearly or perhaps even finished when Bungie decided to cut it.
- Marcus R. Lehto mentioned this level in the DVD that came with Collector's Edition copies of Halo 2.
- Parts of this level may have ended up as part of the level "Sacred Icon." "Sentinel Headquarters" may also be the working title for the final level, as it takes place inside the Sentinel Wall.