Looking for the Foursides, Goldenrods, whatever village or town or city you remembered from video games and that can be thoroughly explored and that are considered "big"
Kinda funny but I remember how vast Minniopolis seemed in The Urbz Sims in the City for GBA and DS and I saw a map this year that looked so tiny, amazing how big it felt at the time
The Imperial City from Oblivion was big-ish but not huge. Blackreach in Skyrim was big too, but stretches the definition a bit, because it depends if you count all the dungeons as expansions of the 'city', what with them being underground
The Imperial City comes to my mind too, especially if you're a theif. It's not big like a modern city, but there's hardly a single door you can't enter, and I just love how so many basements connect to the sewers, it's like you can almost navigate the whole city underground, except you're more likely to get lost down there!
The various mods available more than double the size, too.