Deep beneath the verdant hills and cerulean seas of the surface world, there are caves. Arterial pathways through the bedrock connecting the surface world to dark underworld. Deeper still, penetrated by the lost kingdoms of the dwarves, magma churns, moving the continents on glacial timescales only the longest lived peoples can appreciate. This is the domain of elemental forces of fire and earth, but even they are not the core of things. Beneath this sea of magma is a great bronze egg, spinning at tremendous speed through the viscous muck of the world's guts. At this egg's top and bottom, man-sized portholes offer a means of ingress to a truly colossal work.
The interior of the egg is fixed on a cyclopean gyroscope, built around the pulsing heart of the planet, the Heart of Arcosa, burning as brightly as a star. Everything is built in relation to this molten ball, encircling its intense gravity. The egg itself is 120 miles tall, and and half as wide. At first inspection, Arcosa is abandoned. Eight-foot tall humanoid statues litter every courtyard, and every street corner; art deco sentinels of a dead city, watching downwards towards the second sun in the center of the metropolis.
Closer to the Heart of Arcosa, where the city becomes unbearably hot and gravity is twice as strong, the statues move unimpeded. They travel closer to the core, or back from it, with their surfaces burnished and steaming. They are oblivious to any interlopers, even if attacked or impeded. They swat at interlopers like one would a horsefly. Some of the bronze men lay in disrepair, unable to continue working due to melted bodies. Precious relics of a long-lost civilization are more common here, protected from thieves by sweltering heat.
Nearest the core, Arcosa steals the moisture and burns the flesh of any living thing that dare treads here unaided. Paper browns and carbonizes after an hour, and open water evaporates in minutes. The light from the Heart of Arcosa beats travelers back from below like an enraged dancer, spinning loudly. The bronze men march down into the light with the vigor of a farmhand. Peering between slats in the floor, the truth of their purpose is illuminated by the sunspots they cast against the Heart of the world.
Four rods, each a mile in length, have been inserted into the near-molten core of the planet, and thousands of these bronze men march in lock-step to push these rods and spin the core. Some machination of the machine they operate turns this force into rotation, and that rotation is captured by pillars spanning from the Heart to the exterior of the shell, spinning it with enough velocity to melt rock. That rock then churns silica butter, and heats the surface world indirectly. The rods lie abandoned in large stretches where no bronze men have taken their obvious places.
Who knows what consequences might be faced when these constructs finally give out for good?
