A massive hive like structure that can contain and entertain a human for their entire lifespan. Whether its one massive skyscraper, or multiple thirty-story blocks connected by a web of sky-ways, its a construct larger than most towns. It would seem daunting to map all the passageways, to plan out a settlement for thousands of people, and describe a building unlike anything the players have seen.
Yet a NEST - or other arcology megastructure - is probably one of the better places for introducing new players to the world of Dead and Back's Anarchy Zone. Behind the gigantic walls are very familiar settings. Being largely self-contained and decently populated means there are plenty of alliances and conflicts waiting, aside from simply shooting reanimates. People from all walks of life survive inside the halls, so players are free to make characters outside the basic survivalist mold, and can easily replace them as necessary.
While the scale might be huge on the outside, within the NEST is very familiar territory. Medium to small apartments (many of them single room studios), fast food restaurants, school rooms, theaters - it is like any other city, just without sky. Although many places may be dark or dingy after five years of neglect, most of the interior has not fallen to ruin like exposed structures. Interior green spaces look like a mall's atrium or city botanical gardens, just with roof heights of between three and five stories.
A small city is too large for direct democracy, there will be bureaucracy and competition. Should the doors be opened to other survivors, or must some of the current population be expelled due to over crowding? How should the former property of others be divided among the survivors? Leaders will change, either through clever elections or more violent means, and the players can be their to exert influence, either for their bosses, or to gain some power themselves.
Many new stories are possible because many people survived thanks to the buildings inherent disaster isolation elements. Outside, much of the world belongs to raiders, ex-military, survivalists, and the savvy - though the simply lucky make for a good percentage as well. Few people would think of playing "Conan the Barber", cutting hair across the wasteland. But a stylist that maintains their business within a NEST, and over hears the discussions of the powerful because of it, could end up in some political intrigue. A teacher would struggle not for them-self alone, but with the question of what to teach in the new world, and how to keep a classroom as a safe and inspiring place when outside there is so much danger.