From Nookipedia, the Animal Crossing wiki
The City (シティ Shiti?) is a location featured in Animal Crossing: City Folk, though it is first mentioned in Animal Crossing: Wild World. The city can be reached by riding a bus from the town. Only a central plaza area can be explored in City Folk, housing merchants and services, a theatre, and with access to the Resetti Surveillance Center. Random villagers from out of town, possibly inhabitants of the city, can be seen wandering the plaza and browsing the shops. The villagers that can be seen in the plaza will change every time a building is entered and exited by the player.
Curiously, precipitation in the city will affect the town, even if the weather is different there. Flowers in the town will be hydrated by rain in the city, and gyroids can be found buried underground the next day.
In Wild World
The city is mentioned by several characters in Wild World;
Cranky villagers will sometimes ask the player if they were brought up in the city, while it would appear that the player moved from the suburbs of a city, as hinted by their mother's letters.
In City Folk
The city in City Folk is accessible by bus from the town, which is free of charge and available at all hours. The city's plaza contains a bus stop and shops, such as an Auction House, Shampoodle, and GracieGrace, as well as the headquarters of the Happy Room Academy. Characters such as Crazy Redd, Katrina, and Dr. Shrunk all have their own venues in the city, and they no longer visit the player's town. There is also an Automatic Bell Dispenser on the left side of the plaza, below the Marquee theatre, which functions exactly the same as the one in the Town Hall. The Resetti Surveillance Center can be accessed through the tunnel on the far right of the city, but only when the cones have been moved. A large fountain stands in the center of the plaza, similar to the one that can be built from donating to the Town Fund, but with a unique statue depicting Serena.
A skunk named Kicks can occasionally be found outside the dilapidated building during dry weather, and will shine the player's shoes for 500 Bells. On sunny days, a sea lion named Phineas will occasionally appear next to the fountain and give the player unique items such as pinwheels and balloons. Up to five villagers may roam the plaza, though fewer will appear at night, all of which who do not live in the player's town. The villagers seen in the plaza will change every time a building is entered and exited by the player.
A black market owned by Redd is situated on the left edge of the plaza, and entry is by invitation only. The player can be invited to the store by villagers, other players, or even Redd himself via mail. A one-time entrance fee of 3000 Bells must be paid in order to enter. Redd's store sells rare items and paintings, which are sometimes forgeries. Their authenticity can be determined by Blathers or Tom Nook.
The Marquee is the city's theatre, where players can watch comedy routines performed by Dr. Shrunk, and on rare occasions by Frillard. The player can learn up to four emotions, with the emotion learned being based on the routine that is performed.
The Happy Room Academy
The Happy Room Academy (HRA) have their headquarters in the city. The office is managed by Lyle, who can inform players of their HRA scores, unsubscribe players from the mailing list, and explain about the organisation. A model room is displayed at the back of the building, and high-scoring player rooms that fit the monthly theme will be presented here.
GracieGrace is a high-end boutique that sells high-priced furniture, clothes and accessories. The store's inventory is seasonal, and clearance sales are held near the end of each season. Labelle is the shop's clerk, but occasionally the owner, Gracie will appear to offer fashion critiques.
The Auction House
The Auction House is a building run by Lloid, the gyroid, and is open 24 hours a day. Here, items can be displayed and bid on by players and their friends via Nintendo Wi-Fi Connection. The player can also access their storage from the auction house's checkroom. As the online service has been discontinued, this building is now of very limited use.
Katrina runs a Fortune Shop, where the player can have their fortune read to determine their luck for the day. Katrina can also provide charms once a month, which require certain conditions to be met that can usually only fulfilled by visiting players. Fulfilling the conditions will confer a special benefit on the player.
The city is part of the stage Town and City, a Wii U exclusive stage.