Nests
A nest (or nest town) is an independent city, which does not recognize the rule of Orlis or Wywick. Most nests started out as temporary camps or outposts, and eventually grew into permanent cities as people settled down.
Stereotypically, nests are considered "wilder" or less civilized than other towns, but also more accepting in some ways; they are gathering places for criminals, adventurers, and people with nowhere else to go. There is some truth to this, but individual nests vary greatly in their culture and management due to a lack of any standardizing force.
It is popularly believed that the term "nest" comes from the ramshackle wooden architecture and barricades often seen in these towns, making them resemble birds' nests. In truth, it was originally a short form of "bandit nest" - a derogatory nickname referencing the fact that many of them were founded by criminals.
Development
Many nests started out as bandit camps. Due to the difficulty of enforcing law in the wilderness, it's relatively easy for a band of criminals to set up near a bridge or pass and rob everyone who passes by, with little fear for retaliation from the government. Nests can also grow out of guild outposts, resupply stations, temporary work camps, and so forth.
In the beginning, these temporary camps could buy supplies from a nearby city to sustain themselves. However, as they became more profitable and attracted more members, this became less practical. Travel is dangerous in Empyria; frequent supply runs would attract monsters and (rival) bandits, especially if they carry large amounts of valuable goods.
To reduce their reliance on supply runs, residents would convert the settlement into something more defensible and self-sustaining. Farms, watchtowers, barricades, and so forth are built. Around this time, people also start considering the camp their home; they spend enough time there that they get used to the culture and people, and invariably some of them will want to settle down and raise a family where they are.
Once a full defensive wall around the camp is completed, it can be officially considered a town, and therefore a nest.
Ending Nesthood
While some nests remain independent forever, others eventually join the country whose land they occupy. Some find they've overestimated their resources and cannot hold the nest against monsters forever; others simply want the benefits that come from being part of a larger whole.
Orlis will occasionally send soldiers to threaten particularly large nests on their land, as it sees them as threats to their image of a unified empire. However, nests are by definition inhabited by a bunch of hardened adventurers who've survived in the wilderness for years without a city wall, so it's very difficult to force a nest to do something it doesn't want to.
Examples
Valefar
Location: West Ortesia
Notable Landmarks: Sylph's Shrine, Valefar Academy
Valefar City and its surrounding plains are the territory of the Great Spirit Sylph, who takes an uncommon interest in the affairs of humans and defends the city against monsters and human invasions. As such, Valefar enjoys the distinction of being the largest city in the world, as well as the only city without defensive walls.
Owing to its status as a safe neutral zone, many people move to Valefar to start a new life or hide from their pasts. Plenty of smuggling and shady deals happen behind the scenes, but Sylph draws the line at violence, so if you try to murder someone within city bounds be prepared for a couple magic pigeons to beat the shit out of you.
Valefar Academy, whose sprawling campus takes up the entire west quarter of the city, is one of the most prestigious mage academies on the planet. Many rich Orlisians send their children to Valefar to get a proper education, contributing to the already wide variety of humans that can be found here.