Mars City (Location)

Mars City is a base of the UAC located on Mars, constructed 25 years before the events of Doom 3. Sergeant Thomas Kelly leads the security and defense force of the base, made up of standard Mars City Security and elite Marines. Additional security is provided by Sentry Bots.

The main Mars City complex was primarily composed of offices and labs, as well a break room with a Super Turbo Turkey Puncher 3 arcade machine, in addition to a medical lab and an armory. Mars City is the main facility on Mars, possessing a boarding area for both new arrivals and those exiting the base. Mars City also has an underground maintenance area, aptly called Mars City Underground. An elevator connects Mars City to the monorail station for transport to various other sites nearby.

During the events of Doom 3, the base was consumed by a large invasion from Hell itself, with most of its personnel slaughtered or transformed by the demons. The only survivor was the Marine that arrived just before the invasion. In spite of the invasion, the UAC soon restarted operations on Mars within two years, reconstructing the base. Dr. Elizabeth McNeil was placed at the head of the facility to replace Dr. Malcolm Betruger.

Mars City Underground
Mars City Underground is what keeps Mars City operational. It has a large amount of storage space, maintenance areas, and a set of communication arrays (though abandoned). Most of the Underground workers were very cautious and easily spooked, thanks to the odd noises they hear while working. Before entering the area, there is a security checkpoint headed by T. Brooks. Mars City Underground also has an airlock that leads to the surface of Mars and the abandoned communications array.

Administration
Administration housed the UAC administration on Mars and was the main reporting site for all workers prior to the invasion.

Alpha Labs
The Alpha Labs are a research lab built in the year 2130. Its main focus is to create technologies like the EPD or the Hydrocon. Divided into four sectors, these Labs managed to create extremely advanced technology that humanity could've used for generations, if the invasion didn't destroy most of it.

Enpro Plant
The Enpro Plant is an energy plant dedicated to power the entirety of Mars City and to create the plasma cells necessary for the Plasma Rifle. A massive core powers the entire plant, and subsequently all of Mars City.

Communications Transfer
Communications transfer is a shortcut between the Communications Room and the Enpro Plant. Oxygen tanks were stored here after many pressure failures occurred.

Communications Room
The Communications Room was the main comms area for communication with Earth and any nearby facilities. It was focused through a station on Phobos and directed to Earth itself.

Recycling Plant
The recycling plant is one of the most important facilities on Mars. The main purpose was to recycle the waste products of the Mars City personnel. It was divided into two sectors, with the latter being where Betruger introduced himself to the Marine.

Monorail
The Monorail is a station that housed the monorail train. It was primarily used to transfer personnel from the recycling plant to Area 2 or to the Delta Labs. The main entrance to the Delta Labs was housed by an Automatic turret, which could be disconnected in the security room.

Delta Labs
The Delta Labs is the most advanced research complex in Mars. It housed four sectors and a teleporter, which was the origin of the invasion at the beginning of the game.

CPU Complex
The CPU Complex housed the entire computer database on Mars, and was where the Marine fought the corrupted Sergeant Kelly,

Site 3
Site 3 was one of the primary housing facilities for archaeological artifacts found in the dig sites.

Caverns
The caverns were the first installations ever made on Mars. Its main focus was to discover archaeological artifacts and send them to Site 3.

Main Excavation
The Main Excavation was where the Soul Cube and many other relics were found. It also housed the portal to hell and the Cyberdemon guarding it.

Trivia

 * The window shutters in the kitchen can be lowered, with the lights being turned on, as well.
 * Super Turbo Turkey Puncher 3 makes a reference to previous Doom games by having the original face of Doomguy in the upper left corner, as well as utilizing the same melee animation as in previous Doom games.
 * Mars City is a smoke free area, presumably due to the countless materials that are flammable inside the facility