There is a city, between Between. It floats in the Astral as a free-floating pocket reality, largely disconnected from the rest of existence. It's called Zenith, but no one is entirely sure why, nor sure who built it, or how.

Zenith has a number of unusual qualities. It is, first off, sentient, in some fashion. Communicating with it is frustratingly difficult, but the city moves and shifts occasionally in ways that (while not obvious in their intention) are clearly the product of a singular, intentional will. It forms patterns that are obviously nonrandom. It is, in some sense, alive. Second, while it has been filled with mortal construction over the ages, the base structures of the city are all virtually impossible to damage. From dizzying towers of bismuth and adamantine to the most frail pane of glass, they exhibit a sturdiness normally only seen in potent magical artifacts, shrugging off hammerblows and fireballs with no apparent damage. Bismuth, skymetals, glass, and crystal characterize these structures, all clean lines and mostly inorganic.

The third oddity is, however, the most...noteworthy. Zenith is filled with portals, doorways that lead...elsewhere. They are dizzying in variety, taking every form from gleaming metal archways to gaping, hungry mouths that open in the ground, pools of dark water with no bottom to simple freestanding doors with no locks. They all, however, exhibit something in common. They do not open for free. The prices are varied, and hard to predict; sometimes all it takes is saying "please" in Draconic, while other doors require specific mixes of incense and burnt offerings, or human sacrifice. Some doors take their toll from every traveler, others remain open once the initial payment has been offered. New ones form routinely, and old ones are sometimes subsumed by the city's shifts and movements. The experience of going through a door is harrowing, by and large; intense feelings of fear or guilt are common, as are hallucinations, stress, and mild amnesia. The first passage is always worst, as though Zenith takes a toll for the passage, especially for those who are entering the city through a door from elsewhere.

There are three general variations on where they lead. The first, and simplest, open onto somewhere else on some other world. Zenith has had portals open to virtually every plane, every planet, at some point, though many have since closed. These portals are how the city between sustains itself. They bring in travelers, many of whom proceed to remain in the city rather than risk further doorways. They allow for trade, and easy transport. While Zenith has expansive garden areas, it is largely inorganic, and has to import large volumes of food from more agrarian worlds. In trade, its citizens pay in trinkets that might be almost valueless in their source world, but are precious elsewhere. In this way, the city survives.

The second type of portal leads, rather than to large planes or worlds, into small, isolated demiplanes, some of which have been cut off from the rest of reality for centuries before a doorway opens into them. The rules of reality and natural laws can be very strange, in these little pockets of existence, and travelers from Zenith quickly learn to be wary of anything in them that seems even the slightest bit strange or unusual. They do, however, provide more...unusual imports, which can then be sold in larger corners of the universe.

The third type opens Inside, to parts of Zenith not otherwise accessible, fractally nested inside of the city that it presents as its outermost face. These pocket dimensions are strange, surreal, and often contain magical items of considerable power. They are also, however, dangerous. No one really knows what it is that takes the people who go Inside and don't come out; they don't show up again, afterwards. Those who do return (and are willing to speak of the experience) tend to describe it as a bizarre experience, often involving more direct communication from Zenith than it exhibits in the superficial layers, and sometimes involving strange curses or hazards.