Delta Labs - Unknown: Union Aerospace Research Division

Delta Labs - Unknown: Union Aerospace Research Division is the eleventh level of Doom 3: Resurrection of Evil. Player fights through parts of: Delta 3, Administration, Delta 2B, and Delta 4 from Doom 3, that have been possessed by Hell. This is the most unique level in all of Doom 3, because the entire Delta Complex is in constant dimensional flux with Hell and shows a horrifying alternate version of the area every few seconds and warps the player's vision. Bloody skeletons appear when in flux with Hell and can be interacted with until the flux stops.

Triva
The Main Portal in Delta 4 was destroyed after the Hell in Doom 3. But know one knows how it got fixed.