Nirdalor, a city built around its industry for airship. A city who grew up instead of out, resorting to building on top of its buildings for generations. A city whose centerpiece is a maestrom of design and a miracle of structural integrity.
It isn't a natural part of Zallia, rather it is a city native to Abelay, one of the continents of Ilseron, the planet that had suffered most in the Joining of Worlds. It is one of few places where airship construction, engineering, and maintenance is a huge priority, bringing in people from all sorts, and this now includes curious Zallians.
In my campaign, the party has just arrived here with their own airship, constructed as a reward for breaking a coup and slaying one of Ilseron's most infamous villains.