Ankh-Morpork in Discworld Mud. Sure it's only text, but the city is truly massive. Hell every city in the Disc is pretty awesome. Museums, theatre, your guilds, player housing and stores. Shopping (and lots of stealing). You get to meet a lot of the characters from the books too. Nothing like getting caught by Angua whilst finishing off one of the city's denizens, then having to crawl to a doctor after she breaks your legs for you. Of course you have to spend your time in a cell first.

I spend much of my time as a thief shoplifting in the stores to fill my quota, then hunting down bankers, lawyers, traders, mercenaries, and a few others with too much money for their own good. It has all the great districts from the books, especially the dreaded shades. You can buy stuff from smugglers and other shady characters at the docks. Climb a tower during the full moon to buy stuff at the moonlit market. Many many quests and odd jobs are also available, as well as achievements.

There are seasons, day and night, weather and temperature. You can actually freaze to death, get a nasty cold, or die from over heating. During snowstorms you can't see very far, and maybe not even past the room your in. There are carriages that can take you around the city or other places in the disc, even ferries. You can get all kinds of furniture and many other nicknacks for your homes and stores, which you have bid against others in auction for.

You can become a citizen, run against other players for positions on city council. There are 2 player run newspapers that compete with one another for viewership. There is so much attention to detail, you just don't see these kinds of things in modern games. I wish more games would pay this kind of detail to their cites.