Site 3

Site 3 is the furthest set of caverns excavated by the UAC in Doom 3. This is where most of the artifacts, including the Soul Cube, were found. The player can see tablets that the researchers found which detail the plight of the "ancients" and the first invasion by the forces of Hell. The only known entrance is the elevator that leads to the CPU Complex.

Site 3 was also the location where a statue of the Praetor Suit was discovered in 2122, as well as statues of the Doom Slayer and two Night Sentinels in Doom (2016).

Research Area
The Research area is where the scientists study about the discoveries that were found in the Caverns. The Research area holds the Tablets for further analysis and for guests to marvel at. Not much is known about the Tablets but it is stated in an info video that they were the source of the teleportation technology Betruger utilized. Further study was occurring before the invasion.

Caverns - Area 1
The first Caverns area is home to few valuable findings, because the real story takes place in Area 2. Area 1 houses some locker and research areas.

Caverns - Area 2
The second Caverns area is where many discoveries were found. There are spinning lights with writings on them that were still being worked on. There is also a temple door that leads to the Primary Excavation, the place where the Soul Cube was found.

Primary Excavation
The Primary Excavation is where many artifacts were found. When the demon invasion started, it's where the second portal of Hell appeared: the Hellgate. The Hellgate was guarded by a Cyberdemon.

Levels that take place in Site 3

 * Site 3: Analysis Facility
 * Caverns - Area 1: Excavation Transfer
 * Caverns - Area 2: Artifact Excavation
 * Primary Excavation: Artifact Dig

Trivia

 * Site 3 takes place below the Delta Labs.