: If the Gravemind room was literally present in-game at the bottom of the
: Library shaft that would be a strong indication of Bungie's intent, but it
: isn't. And you don't even need modders to figure that out (trickers have
: been all through that pit, it's just an ordinary pit).

Actually it is there in the fully loaded model. It only loads when the cutscene takes place which is why modders didn't see it. Arguing it's not there because modders didn't get to it is like saying the Cairo station Pelican hangars aren't there when you're in the armory. Those portions just aren't loaded at the same time, but the meshes do connect in that way. Same with the Library.

Here's a perspective shot of the entirety of the level Quarantine Zone loaded all at once. I've marked some key landmarks for reference since this perspective is never seen.

I oriented it so you could see the Gravemind Chamber below the Index area. In the small inset, I loaded the Halo Control Center from the first game for comparison.