Black Mesa Research Facility
Where it all began, the research center built out of a military base in Black Mesa, New Mexico. It becomes a large complex of laboratories, an Anti-Mass Spectrometer, and more questionable structures by the time Dr. Gordon Freeman first steps inside. This facility is the major setting for Half-Life, with Xen being the other large setting.
The structure is largely concrete on the outside, and apparently metal in the laboratory areas. The largest change in design occurs when going into the industrial area.
In the laboratories, the ceilings are high, corners can be curved, and computers line several walls. The facility is well-ventilated, so vent sections can be used to get past blockades (and tend to be full of headcrabs). Overall, the architecture in the laboratory section is simple, designed solely to serve the lab's function.
Outside, the structure is more clearly a military base, with its heavy use of concrete and metal doors. The mesa that the facility seems to be built into has a relatively awkward shape, which allows for sheer rock faces to serve as barriers and stone archways to add to the atmosphere.
Since Black Mesa is in New Mexico, the surrounding area is largely desert. There are several other mesas surrounding the facility, some of which can be seen in the cliff sequence about halfway through Half-Life. Water is fairly uncommon outside of laboratories, or the one river Gordon swims through. Therefore, water should be used minimally, or as something more dangerous such as radioactive waste.
Lighting, where it works (the accident causes several power problems), should be clean and sterile. Whites and soft blues tend to give this impression best. Outdoors, the sun should feel hot- this is New Mexico, after all. A near yellow-orange color can produce this effect. Hazard lights are turned on in several places where damage is higher, such as the office area, and can provide a good lighting situation for sudden attacks.
Sounds can vary from military radio messages, to laboratory activity sounds, to alien cries. Which one is appropriate depends on where the player is, and what has already happened- alien cries would seem highly out of place if no aliens have shown yet. In general, the sounds are used both to create a horror feeling and to warn the player of what may be to come.
Virtually every creature that appeared in Half-Life made its way into Black Mesa. Vortigaunts, headcrabs, and zombies are commonplace. Ichthyosaurs occasionally populate the waterways. Some boss creatures also make their way into Black Mesa, while some larger ones remain in the Xen world.
Along with the alien creatures, soldiers and assassins appear to deter Gordon. Coming to his assistance are the scientists and the security guards. However, for the bulk of the game, Gordon is on his own, followed only by Gman.