1. Town exists because 10-foot-high waterfall blocks river traffic. Portage of goods is simple, and several hotels / taverns / flophouses sprang up there. Teamsters Guild runs the place behind the scenes. River is navigable in both directions.
2. Hot spring in hills outside of town attracts rich and nobility to take a cure for their aches and pains.
3. "Singapore": highly-defensible harbor (on island?) between two rich nations / cultures. Local trade center and international merchant nexus.
4. Capital city of prosperous nation, with resulting political plot hooks.
5. Local weather / landforms / whatever just happen to be right for growing mulberry trees and silkworms - or something else rare and valuable - so the concentration of wealth draws adventurers and foppish rich people looking to show off.
6. Dwarven city in Lonely Mountain surrounded by Human and Elven lands. Cosmopolitan multi-racial culture very unlike the provincial locals all around.
7. Town was built on / into / under a floating earthmote. Prominent piece of public architecture: the Staircase Bridge.
8. Tourist attraction, anything from natural phenomena (Old Faithful) to holy relics of a saint (St. Patrick) to famous building (Leaning Tower of Pisa).
9. Town was burned down by an accidental fire that got out of control, a few years back. The place is rebuilding - with a much more effective Fire Department and Fire Chief in charge now.
10. Local graveyard is said to be haunted, AND necromancers from far and wide keep showing up to "investigate" the place. "Obviously, they are up to no good," say the locals.