Site 3

Site 3 is the furthest set of caverns excavated by the UAC in Doom 3. This is where most of the ancient artifacts, including the stone tablets and Soul Cube, were found. Contrary to its name, Site 3 was actually the location of the first human base established on Mars. The last portion of Doom 3 takes place at Site 3.

Site 3: Analysis Facility
The Analysis Facility is located at the surface of Mars. This is where UAC scientists study the artifacts found in the caverns. Here the player can see the stone tablets which detail the plight of the "ancients" and the first invasion by the forces of Hell. The only known entrance to the Analysis Facility is the elevator that leads to the CPU Complex.

The research area of the Analysis Facility contains the Tablets for guests to marvel at and for scientists to examine. The four tablets go into detail about the Ancient Martian's teleporter technology, the demonic invasion, and how the Soul Cube was used to stop the demons. Scientists in the Delta Complex used the information on the stone tablets to construct the Delta teleporter devices, not realizing that the tablets were in fact warnings.

The Analysis Facility leads to the first Caverns area.

Caverns - Area 1: Excavation Transfer
Caverns Area 1 was the very first human base established on Mars. It now serves to transport artifacts and materials discovered in Caverns Area 2 to the Analysis Facility on the surface.

Caverns - Area 2: Artifact Excavation
The second Caverns area is where many artifacts were found. There are spinning lights with writings on them, that were still being worked on. This area also houses strange egg-shaped levitating devices with unknown functions. Beyond that is the Room of the Stars, the walls of which are filled with glyphs, and the ceiling contains what is apparently a map of the solar system. There is also a temple door that leads to the Primary Excavation.

Primary Excavation: Artifact Dig
The Primary Excavation is where many artifacts, including the Soul Cube and the stone tablets, were found. This contains the Burial Chamber for the Hero. Another set of tablets like the ones seen in the Analysis Facility can be found here (it appears that there were originally two sets of the same four tablets on either side of the chamber, and the UAC took one set back for study). The walls of the Chamber and the passageways leading to the Chamber are covered in glyphs.

Beneath the Primary Excavation is the demonic Hellgate. It is guarded by the Cyberdemon. This is where the final battle of the game takes place.

Levels taking 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.