Take a look at this city map, and tell me where it came from. If you've been playing D&D for a long time, I bet your answer is going to be either "City State of the Invincible Overlord" or "City State of the World Emperor." WRONG!
But I betcha that those maps were based on something like this, because this is a map of Pompeii's Roman ruins, as excavated. Chris Kutalik (of Hill Cantons) pointed out on Google+ that this map would make for an awesome megadungeon, which is more creative than I was; I was just sitting there thinking, "wow, all those little buildings in CSIO were probably supposed to be internal walls inside insulae" (in other words, the mall space under a big apartment building).
All these years I had a completely incorrect impression of the City State, assuming that the Judges Guild team also realized that the archaeological map showed insulae rather than many small buildings.
Take a look at this site, using the left side to click on the different "Regio" links, and you'll find yourself in the middle of an awesome city resource!
PS, I do not know how to link to Chris's actual G+ post, so I linked to his awesome blog.