Gotham City is a place of shadows. Mystery. Intrigue. No one really knows what goes on in its alleys and catacombs, the closed doors in city hall, the lair of the enigmatic Batman.
So of course, everyone talks. If you get Gothamites in the right mood, they will prattle endlessly about what they've heard, seen, or suspected of their city. This is something I encourage; you won't find many better leads. Once they feel they won't be mocked, they're especially eager to impress an outsider with the mystique of their home.
They say that Gotham has two sewer systems. The first was infested by alligators and criminals so badly that the city built a second one using misappropriated road maintenence funds (so they wouldn't have to clear them out). This newer network hosts the city's feral penguins (if those even exist).
They say that the reason it rains so much in Gotham is because of a Native American curse on the land, or a cult of vampires that control city hall. They say that enough gold has been dumped into the Finger River over the years to make Fort Knox blush, but there's a reason no one will retrieve it. They say...many things.