The Machine is the name of both a mechanism of potentially infinite size and the parallel dimension that contains it. Its age and origin is unknown, but various writings and archeological findings from across the galaxy imply it may be at hundreds of millions of years old, predating any known civilization.
All of The Machine is an interior space. No sky or ground can be found no matter how far one travels vertically. Gravity is inconsistent in both strength and direction, seemingly having no pattern to its pull although one must travel far to feel its effects shift. Temperature, air pressure, humidity, and air composition also varies.
The parts and mechanisms of The Machine vary greatly in size and function. Most common are gears and pistons, which range from intricate hand-sized parts to monolithic building-sized slabs of metal. Pulleys of chains, hydraulic pumps, and rotating shafts also populate the moving parts of The Machine, all connected and rarely stopping.
In sharp contrast to the metal machines are the pulsing masses of flesh. Veins, muscles, and walls of skin are found webbed between the machines, forming dark, wet tunnels. The flesh is a mix of red, purple, and blue; Essence, a thin blue fluid, flows through the veins in lieu of blood. Structures and spires of bone occupy some of the more empty areas.
Some areas of The Machine are very clustered, with only thin tunnels found between massive heaving machines. Some of these tunnels are comprised entirely of flesh, stretched skin around bulging, pulsing veins; others are more domestic hallways of metal grating and polished walls of black marble.
Other areas are vast and empty with thin metal bridges stretching over abyssal chasms of shadow, where moving machines and rolling chains are only barely visible in the distance.
Forests can be found within The Machine. Where Essence spills and dries, plant life of a great variety grows including moss, grass, vines, and trees. These areas are like massive subterranean caves - some art dark and dimly lit, while others simulate sunlight through special Essence lights.
Rare, isolated locations within The Machine are intensely heated, full of molten metal and massive fires. Here, new parts of The Machine like gears and pistons are forged and boiling steam is redirected towards other areas.
Vast fields of red clay from which some Machine inhabitants are formed.
Many people find themselves inside The Machine, be it by intentional search, accidental discovery, or an overt outreach by The Machine itself. Most people brought into The Machine become part of it, literally: after an poorly understood and often time-consuming process, people become gears, pistons, or pulsing veins, blood replaced by Essence.
After full Incorporation, people often return to their original existence in their unharmed physical form, but an aspect of their mind and soul remains within The Machine, forever part of The Work. Their Work within The Machine can always be felt, and a full return to their awareness of The Machine often returns during sleep.
Overseers are large worm-like creatures native to The Machine. They are proficient in navigating tunnels through the machine and intrinsically know the function of all moving parts near them. Instinct drives them to maintain The Machine and repair or replace any malfunctioning parts.
No writing exists on the life cycle or reproduction of the Overseers; some believe that certain people Incorporated into The Machine are transformed into Overseers.
Special clay that can be shaped into bodies for Machine workers (it's what Joel is now made of).
Essence is a luminescent blue fluid produced within The Machine. It can serve as industrial lubricant, lighting, or hydration for biological elements with specialized machines modifying its properties. Its chemical composition and origin are unknown. As stated, Essence leaves a residue that spurs plant growth in even otherwise barren areas.