In an age long past the inhabitants of the planet GranKra paved over their world with concrete. Know who live know why for certain but the legend is that they were infected with a ruinous meme, a weaponized madness. They smothered the native biosphere with a planet sized complex of tunnels and towers. When their manic work was complete they entombed themselves somewhere deep and hidden and they vanished from history.
For uncounted years Grankra lay empty and bare, its cement towers gently crumbling. This age of quite decay came to an end with the coming of the reclaimers. The endless miles of damp stone corridors are an ideal environment for Scollapendrites, centipede-like aliens. The major issue they experienced was the complete and utter lack of soil. Together with the Orn, strange fungal sapiens they have managed to bring some measure of life to this desolate world. They are aided in no small part by the Church of the Holy Vermin, whom have deployed several of their vermin engines to help repopulate the planet with crawling things.
Scran City, also known as the city within the city is the planet's capital and only spaceport. It occupies the topmost layers of the concrete labyrinth. It is a sleepy burg, with little heavy industry and only modest interplanetary trade. Most residents work in agriculture and child rearing. Below the city is one of the most extensive Motherlands in Reclaimer space. On the outskirts of the city are the fungal farms in damp stone chambers. Beyond the farms are the vermin wilds where the vermin engines churn out vast hordes of critters.
The towers are a perilous vertical environment. The tallest spires are delicate stone needles built beyond the limits of common sense. Space ships moor at retrofitted spars lower in the complex where the structures are more sane and stable. The upper reaches aren't abandoned however. The Wirescape is a district of artists and bohemians above the city. Tight wires between the towers provide high flying roads (humans might find these roads hard to navigate, but Scollapendrites scuttle along with ease) . One of the foremost arts practiced here is architecture, by necessity. Retrofitting the narrow towers for habitation is no mean feat. There is tension between the architects and the more grounded folk. After all architecture is what led to the planet's demise in the first place.
Farming on GranKra is a challenging prospect. There is no soil and little open ground. The Scollapendrites have resorted to mycoculture with the help of the Orn. The Orn use their versatile metabolisms to break down any organic materials, including the concrete. In return the Scollapendrites eat the pests that feed on the Orn, and more rarely, the Orn themselves.
The most famous fungal farm is the garden of the dead. This large chamber is where all deceased Scollapendrites are interred. The dead serve as their own ephemeral tombstones, their bodies sprouting colorful mushrooms and fungal threads. The Orn here act as archivists and guides, helping the living with their grief and keeping the memory of the dead alive. It isn't the most productive farm but its products are eaten during special festivals to honor the dead.
The large Orn presence on the planet has led to an infestation of those other fungal Sapients, the not Orn. These mycological rebels parasitize the Scollapendrites in an insidious fashion. They grow inside the their carapaces and take control of their bodies, using them as puppets. They spread by growing fruiting bodies that release spore, preferably from a high place to infect as many as possible. That said, they don't seek total domination, preferring to manipulate Scollapendrite society from the shadows. They are hunted by the worm paladins, a militant sect of the Church of the Holy Vermin that use trained worms to detect them.
Beneath the city are the Motherlands, a semi wild cave complex that hosts many Scollapendrite Broodmothers, the large breeding females that give birth to all Scollapendrites. Each Broodmother has a carefully tended patch of territory. They feed on cave vermin, but there is barely enough to go around. The wardens have to bring down additional food and moderate disputes between cranky mothers.
The Vermin engines are ancient Floozy devices. They are complex bio-reactors that can take in raw elements out of the environment and synthesize new life forms. They are powered by exotic energies and have been running for thousands of years. Though the Church of the Holy Vermin postures as though the engines do their bidding, the truth is they have been running their own programing since they were discovered. To protect the city from potentially dangerous vermin, the engines are housed beyond the fungal farms, deep in the concrete complex. There are three engines arranged in a trefoil pattern around the city. They are known as the Engine Enigma, the Engine Vermiform and the Engine Corpulent. Near each engine is a shrine with the same title, where priests of the church monitor the output of the engines. The area around the engines is known as the vermin wilds, and it is sparsely settled with hunting camps and waypoints on the path to the vermin shrines. The creatures that emerge from the vermin engines are unpredictable. Each engine has certain morphological quirks and body plans that it favors. Most creatures die before they can reproduce, but a few species have established populations.
The Engine Vermiform belches forth an endless wave of worms. The area immediately around the engine is a gyre of frenzied predation as newly born worms slurp up their smaller siblings. The survivors then squirm out into the labyrinth.
The Engine Enigma weaves delicate gossamer jellies. Some shimmer with phosphorous, while others are invisible. Most have venomous, often psychedelic stings.
The Engine Corpulent makes creatures that are soft and fleshy, moist crawling skin bags. They are usually easy prey for the Scollapendrites, so the wilds Corpulent are the most settled of the vermin wilds. They are not all defenseless however. The larger ones are capable of ferocious bursts of speed and strength.
The Caves of Codex are an unusual formation near the Engine Enigma. This vertiginous cavern complex is covered with alien script. Though some in the city in the city wish to study it, the Church of the holy vermin believes the writing could be an infection vector for the memetic agent that caused the towers to be built. They have been sending teams of acolytes to chip the words away, but the area this close to the Engine Enigma is hazardous, so the work is slow.
The lowest levels of the complex are damp and flooded. They are haunted by the troglodytic ghosts of the planet's old biosphere, simple dead eyed fish like things that live and hunt in the dark. Somewhere down here there is said to be a vast lake known as the Sump. And in its still and fetid waters there is said to be a leviathan worm that is growing ever larger in preparation for the day it will turn the planet above into rubble.