Underneath the surface of the planet, deep down in the depths; passed where people fear to venture; passed all known knowledge; massive tolls push great wheels that turn huge cogs of the machine that powers the world.
The parts of the unimaginably large machine all move, and whirl, and pump, and click throughout the ever expansive catacombs, high-vaulted chambers that look neither carved nor natural, only apart of the intricate machinery itself.
Smaller creatures move smaller wheels and smaller cogs at different points along the machine, all of them hard and worn from their years of labour. Every one of them driven by whipping slave masters that looked even harder and more worn, wearing leather hoods and snarling with hatred as they crack their whips unmercifully.
Driving the slave masters, were even more menacing figures, standing in the shadows of the caves, looking on in silence; their glowing eyes watching for any slack in the eternal workings of the machine.
Occasionally, one of the shadowy figures would bolt out from their hiding and swooped down upon a slave master who's whip was not snapping as often as it should; kicking and screaming, the slave masters would be carted off, gripped in the talons of the screeching creatures as horrid wings carried them up into some high ledge in the ceiling to be feasted upon. Just to make sure the machine was working to maximum efficiency.
Through the workings of the machine; the cogs, wheels, shafts, pistons, axles, and other various parts deep down into the world's core, the heat and motion caused the soft stone of the center to melt and churn into molten lava; the life blood of the planet.
And as the sea of heated rock moved, so did the entire world, thus creating atmosphere and environment to allow life to survive and flourish on the surface.
But this is only a by-product, a happy coincidence of the true purpose of the machine.
For sitting at the machine's end, the machine beginning, was the most terrible of beings. A fat, lazy, dirt covered old man, with a big round belly and a ratty, sooty beard. A wizard.
It was he who had thought of the machine; he who had forced the creatures of the sub-terrain into building and running it. For eons he had threatened them with his magic to construct his great machine. And for eons more had he enslaved them to run it with their sweat and blood.
A machine built for a selfish purpose. For in the end, the machine, and all its systems that ran thousands of leagues under the world's surface, and created enough heat to melt the core of the planet, also ground the wizard's coffee beans to the perfect consistency.
Wizards love coffee.