Underneath a small city in Europe, there is a Machine.
It hums slowly underneath the town, practically silent to all. While the few who can hear it, quickly go mad from the sound of truth.
The sound of bone snapping, screams of pain and pleasure, metal scraping against metal. Sounds of sinew forcefully knit and flesh quickly sharpened, alongside the draining of vitreous fluid and blood.
Some manage to keep sane, but all of them snap when they become unable to hear it, as if somehow, by coping with hearing the Machine, they cannot hold onto their frayed sanity without it.
I don't know whether it is the machine's original function or a mere side effect, but the machine makes the town thrive. Some of the blood seems to siphon into the surrounding farms, fertilising the fields better than any synthetic growth formula can.
I don't even know what the Machine's original function is. Parts of it seem to refine, boil, distill and these fluids go to another part of the Machine. It mutilates living humans, cuts them open, takes out their organs and injects them with some strange cocktail mix of drugs, always keeping them alive for as long as it can. Sometimes, it attaches new limbs or the drugs given causes a irreversible change in their physiology. Other times, it replaces the organs with something different entirely, something that the Machine had created itself.
Many of the.. creatures down there can no longer be called human.