Astropolis

Astropolis
In all the World there is no other place like Astropolis.  No one knows who built the Floating City, when they built it or even why.  Some people believe Astropolis is a fragment of the Old World that survived the Godfall.  Others believe it was constructed by the Mechanicals that maintain it for some mysterious purpose of their own.
For centuries, no one knew Astropolis existed.  Then, one day, the Floating City was there, drifting miles above the Icacian Ocean, broadcasting a general welcome message on various comm-frequencies.
The first people to set foot upon Astropolis were adventurers, explorers and opportunists.  Most of these initial encounters ended badly; usually with the offending adventurer jettisoned from the city's underbelly. 
The first person invited to permanently reside in the Floating City was an itinerant sage named Nerice Grimshaw.  She was eventually awarded the title, First Mediator, and acted as an intermediary between the city and its growing population.
Today, Astropolis is home to thousands of people. Most are visiting students, attending the city's famed universities, but there are several hundred permanent residents.  The city drifts above the World, unimpeded and inviolate. Some nation-states and Cultures have attempted to claim it for themselves, but all hostile actions directed against Astropolis earn swift and deadly reprisals. When the Emperor of Shu declared open war on Astropolis, attacking the city with ancient ray projectors, Astropolis's response was to wipe the Empire of Shu off the map.  It did it in less than three hours.
Life on Astropolis is safe, idyllic and cerebral. The city teems with scholars and philosophers. There are museums and universities gallore, but a dearth of religious institutions or more visceral amusements. The essential needs of the city's residents are taken care of by Astropolis and its Mechs. No one in Astropolis ever goes hungry and illness is very rare.  Short-term visitors are welcome and the city has become a major transport hub, especially for travel to the Open Moons.  Long term residency is granted upon successful completion of an intense academic examination. Permanent residency is extended by the city itself to a select few and is considered a great honor.
Visitors and residents to Astropolis alike must submit to a painless injection that allows the city to monitor their whereabouts and control their access to metropolitan areas.  No exceptions are made.
Law and order are maintained by Mech drones controlled by the city intelligence itself. Minor offenses are punishable by fines and removal from the city. Those who commit major crimes find themselves being ejected from the underside of the city, to fall to their death.
Adventurers seldom come to Astropolis, but often find themselves employed as agents of the city or its residents via intermediaries.  The Floating City has a voracious appetite for new information and technologies and often hires individuals to acquire both.