D&D is always a work in progress. Everything is constantly under development - it's like music that way. So, here is Gumei again, with the benefits of several months playtime.
There is a city on the edge of a far mountain range ringed by pink walls a mile high. Twelve years ago, the gate to the city opened and treasure-seekers and fortune-hunters galore piled into the city. Some of them made it out, bringing with them terrifying stories and incomprehensible devices and lore. And more came to the city, supporting the adventuring class constantly picking through the ruins.
The city has many ways of killing people. The first is perhaps the least obvious: the city never sleeps. In great chunks, city blocks lift up, rotate, translate, and settle back down. There is no pattern to the city's movements, at least none that the wizened sages who have settled in Gumei can find. Through the years and sacrifice of brave civilians settling in unknown city blocks, several regions have been established where the city does not change, or at least does not change in a drastic way.
Threshold contains the sole open city gate and it is guarded jealously by the Pink Wardens, former treasure hunters who realized that more money and power could be gleaned from taxing everything crossing the city's gates. They are hated and feared by those who unfortunately live in Threshold and are constantly under their sway. Pink Wardens all use halberds with additional adornment depending upon their rank. The buildings in Threshold have mostly been cleared of rubble and value, leaving empty concrete shells adorned with huge, metal sculptures of creatures that were once alive. Or are simply very patient.
The Street of Blue Lamps is one of the largest stable areas of the city, as the central Street and several blocks in each direction have never seemed to move. The Street is lined with glowing balls of cool, blue light and fountains spaced intermittently along the concourse provide music and fresh water. The buildings here were all built by residents with imported timber. Policing the inns and service-providers in the Street of Blue Lamps, the Knobbleheads are the self-fluffing neighborhood watch with a patented problem-solving strategy of sapping it on the head.
Terminus is the great subway station beneath the ground. Levels and levels of improvised storefronts, boutiques, and clinics. Anything can be bought and sold here, as long as the Wool Merchants get a piece of the take. A mafia with very poor taste in clothing, the Merchants say they control the action below ground. Of course, there are limits to their power. Below Terminus, the great tunnels reach to every corner of the city. The lights don't work very consistently, though, and there are a great many terrifying things that lurk in the dark.
The last of the civilized districts is Watermill, where the mighty river flowing from the mountains crashes through the sluices into the myriad pipes and tubes siphoning away the water's flow for purposes unknown. Quarters are cramped, wedged in between the pipes and scaffolding, and everything is grey or brass. In this industrial paradise, the Dargrim Institute and the Engineers compete to understand the city first. The Institute is a liberal arts college studying the underlying principles of the phenomena found in Gumei. The Engineers have little interest in the why's and only the how's of the devices and esoteries looted from the city. Both are ruthless in their pursuit of knowledge.
There is exactly one place in Gumei where grass grows and plants flower. However, plants are not the only thing that grow in Statuary - the district is named for the ever-increasing number of statues of horrified people and creatures that line the perimeter. Those few who have survived crossing the district after dark speak of masked Moon Cultists with a strange tube that turn people to stone. They cannot be found in daylight, leading some of the wizened scholars of Gumei to conclude that they must be allergic to sunlight, or can only eat moonbeams, or are very good at hiding.
In a city with so many ways to kill people, it is only expected that the children of those consumed by the city have somewhere to go. Unusually, children born in Gumei never get lost, nor do they seem to be surprised by the constantly shifting network of city blocks and access ways. In fact, they seem to be able to use any access point to appear anywhere. And they call Radiance their home. Built in a deep, flooded bowl, Radiance spirals around a forsaken carnival ground visible from almost anywhere in the city because of the giant Ferris wheel (powered by existential terror) at its center. The water is at times water, lava, acid, or simply an illusion, and the buildings sticking out of the murky depths are prowled by strange half-robots and silver-spinning mirror machines. Strangely enough, the city's minions seem to leave the urchins well enough alone.
Most of Gumei, however is not settled in even a loose sense of the word. Some great cataclysm wracked the city, toppling the once-great spires. In the ruins of these once-great buildings however, some truly amazing devices have been discovered - from wands that disintegrate metal to cloth lighter than silk yet stronger than steel. While the rest of the city is a self-serving murderopolis, the treasures found in the Ruins are worth it, to most. These artifacts are not without their protectors - from the flesh-eating green mold, the ambushing mold spiders, the yellow demihumans with long pointed teeth, and the surprisingly inopportune earthquakes, more have died than returned with treasure.
Last is the jewel of Gumei - Bulwark. Surrounded by a mystical barrier, a full quarter of the city remains standing, untouched by the cataclysm. No one has yet been inside, but through the yellow shield tall spires, flying metal machines, and strange floating orbs rise and fall. The journey to the field's edge is a dangerous one, but the lure of unspoiled goods has caused several well-known scholars and adventurers to waste their entire fortunes trying to gain entry.
Getting About
There are routes, mentioned earlier, between the major districts. These are (mostly) unchanging routes allowing slow but reliable transit from place to place. Those seeking a quicker or riskier route can contract with the urchins, who are always lurking about to take them through a back way.
Additional Threats and Points of Interest
Feral Infant Syndrome - sometimes children get the syndrome. They become violent and mischievous and will usually escape into the gap between spaces, only to reappear, years later, as one of the more violent urchin leaders in Radiance.
Turf wars between the various factions - the Wool Merchants control the wealthiest district and both the Pink Wardens and the Knobbleheads are seeking to move in on their turf. A war between the Dargrim Institute and the Engineers could lead to wide-scale murder and destruction, as both wield terrifying powers and artifacts.
Mutating urchins. Some of the urchins have gained the ability to alter the space they exit as they leave it. For example, chest-bursting someone they don't like. Remember that the oldest urchin is 12.