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 Biodome Complex
The Biodome Complex is is a location featured in Opposing Force in the chapter Vicarious Reality. It is a large facility that contains a series of simulated environments where captured aliens and flora are kept and observed in artificial recreations of their natural habitats. Alongside these enclosures are laboratories where scientists perform studies and tests on the creatures in closer detail.
 Materials Transport
The Materials Transport is featured in the Half-Life chapters Power Up and On A Rail, as well as the first map of Apprehension, the Opposing Force chapter Friendly Fire, and the Decay bonus chapter Xen Attacks.
A mostly industrial area, the Materials Transport consists of a network of dilapidated monorail trams extending deep beneath the facility. It also features several hangars, ordinance facilities, maintenance areas, and offices.
Most sections of the Materials Transport features several trams, partially flooded areas, and prominent Xen wildlife. Some parts are still in use while others are in a dire state of disrepair.
The HECU firmly holds the area near the High Altitude Launch Center. Along the Materials Transport tracks, they have set up several artillery pieces, and are heavily attacked by Vortigaunts. They also wrote on the wall many taunts directly addressed to Freeman, sometimes rather misspelled.
 Track Control
Part of the lower levels are located under a waste processing area located near a small flooded area under Silo D, where the Tentacles have their roots. This is where Freeman starts his tram ride trough the Materials Transport at the end of the chapter Power Up after battling a Gargantua. There can be found Track Control where the G-Man is seen, and powered by a partially flooded Power Generator located below and accessed through a large elevator in an area controlled by a large platoon of HECU Soldiers, and that Freeman must restart. That area is isolated from the rest of the network by concrete blocks put on the tracks and is also filled with Vortigaunts and Houndeyes.
 Lambda Sector Transport
One side of level B is used for a Secured Access of the Lambda Sector Transport, linked to Sector F. This area is not controlled by the HECU but by the Black Ops. Located beside the tracks are offices where can be found the offices of S. Jones and S. Reardon (a nod to Gearbox employees Sean Reardon and Steven Jones), a small lobby with a glass roof, a meeting room with a video projector, charts for the Displacer Cannon and office B-591FG containing a "Employee of the Month" picture of Gordon Freeman. Above the offices and near the building where the tracks can be accessed is also found an Ordinance Storage Facility where the Mark IV Thermonuclear Device is first seen in a truck. The offices are connected to the surface by a deep hole created by an antenna that collapsed, where a generator can be found. One vent found near the tracks directly links to the Level A of Sector F, where Shephard witnesses Gordon Freeman's departure to Xen.
 High Altitude Launch Center
The High Altitude Launch Center is a location featured in Half-Life in the chapter On A Rail. It consists of Silo E, a silo converted into a fully-functional satellite delivery rocket launchpad (the Satellite Rocket Loading Bay), and the Launch Control building. This is used by the Lambda Team, with the help of Freeman, to launch the satellite that later help revert the Resonance Cascade.
 Ordinance Storage Facility
The biggest of the three Ordinance Storage Facilities seen in the four games of the Half-Life story arc, this area covers the Opposing Force chapters "The Package" and Worlds Collide, as well as the Decay bonus chapter Xen Attacks. It is separated from Sector G's Hydro-Electric Dam by a small desert land accessed from the dam by a duct system leading to exit H-287GQ, and connected to Sector E Materials Transport through its underground parking lot. The outside is controlled by the Black Ops that set up a mortar on one roof, but it is mostly swarmed by Shock Troopers, Voltigores and Vortigaunts. Inside, the buildings are partially destroyed, and a Black Ops Apache is targeting a Voltigore. On the ground floor and beneath the facility is a multi-story parking lot where the Black Ops are fighting further Race X creatures, and where they set up the thermonuclear warhead that will destroy Black Mesa, finally activated by the G-Man in person.
The Vortigaunts X-8973 and R-4913 are also sent earlier by the Nihilanth to retrieve Xen crystal samples in the part of the parking lot located beyond the gate present near the bomb's truck. Under the parking lot is Storage Unit 04, a freight area filled with crates and containers, and accessible from the parking lot by an elevator. The place is also heavily guarded by the Black Ops, also attacked there by Race X creatures. A practically abandoned industrial area with giant fan vents located further underground contains a Race X portal that, when apparently powered by hundreds of Sprites, brings in the Gene Worm soon defeated by Adrian Shephard.
 Sector E Line
 Sector E Subsurface Transport
Level A of this Black Mesa Transit System section can be accessed from Sector C Line, where the G-Man is first seen in Half-Life, and leads to an unnamed area where the first Shock Trooper a zombie security guards are encountered.
 Behind the scenes
- According to early builds of Half-Life, the Sector E Materials Transport area and its tram were originally very different, and apparently not in such a state of disrepair.
- The Half-Life texture files features three signs with "
c2a2a" in their names. One has "Sector E Subsurface Transport - Level A" written in blue, another has "Sector E Loading Bay" written in orange, and the third has "Subsurface Materials Transport System" written in red. When going through the map named "
c2a2a", which is the second map of the Half-Life chapter On A Rail, none of these signs can be found. The "Sector E Subsurface Transport" sign can however be seen near Sector C Line in Opposing Force, in the area where the G-Man is first seen in Half-Life, thus bringing back this name into the released games but in another location.
- Under a HECU outpost in the Materials Transport (in the map "
c2a2c") can be found an Easter egg placed by the mapper, Dave Riller, consisting of his last name in relief.
 List of appearances
|Half-Life story arc journey||Succeeded by|
Biological Waste Processing Plant
Black Mesa Transit System
|Half-Life: Opposing Force story arc journey (1)||Succeeded by|
|Half-Life: Opposing Force story arc journey (2)||Succeeded by|
Waste Processing Area 3
|Half-Life: Opposing Force story arc journey (3)||Succeeded by|
|Half-Life: Decay story arc journey||Succeeded by|