I suspect every GM has tried their hand at designing at least one dungeon, if not dozens. At some point, most GMs even start toying with the idea for a world, even f it doesn't get very far in the actual design. But designing an urban environment/setting has been the downfall to many a GM. Even though it is much smaller than a country, the details required to bring an urban environment to life are daunting.
Why not let the work be done for you, much like Gabor Lux has done with today's Deal of the Day - Baklin, Jewel of the Seas. Normally 8 bucks for the 72-page Baklin setting guide and adventure module in PDF, until tomorrow morning it is marked down to $3.20.
“Oh Baklin, Jewel of the Seas, great gateway of Erillion! Minstrels sing of its wealth and marine power; and of the refinement and taste of its magnates and nobility. Minstrels of all kinds, of course, are prone to grandiloquence; and perhaps Baklin is neither as mighty nor as fair as the ballads claim. And yet, there is reason the minstrels sing so, for Baklin has wealthy patrons, its fleet is not inconsiderable – and are its streets not the loveliest within so many weeks of travel? Indeed, those who brave the high seas often believe so… and they will gladly pay for a song to remember their visit.”
A 72-page setting guide and adventure module for low to mid-level player characters, Baklin: Jewel of the Seas describes a medium-sized merchant city, including its rulers, criminal underworld, establishments, and three-level Undercity. Baklin is meant as both a campaign hub a party can depart from and return to (with numerous hooks for wilderness adventures), and as a complex adventure location of its own. It can be used along with the materials published for the Isle of Erillion mini-setting (Echoes #02–05), or it can double as almost any neutral-aligned port town in your own setting.
In any case, Baklin is meant to be played: it is focused on city intrigue, exploration, and dungeon crawling. Go shopping for great deals in port or at the stores of the reclusive Masters’ Guild; be careful not to fall afoul of the Sea Laws or anger the Knights of Yolanthus Kar; discover what lurks in the Tower of Gulls; and brave the Shrine of Roxana and the Thrones of Judgement!
This is two identical-length modules in one: a city guide with 39 major locations and a dungeon setting with 112 keyed areas, connected and bound together via multiple secret entrances, plot threads, and NPC agendas.