Here's a bunch of REAL short descriptions of adventure ideas that work well in a city:
Second-story jobs, picking a pocket and finding a map, searching the tunnels under the city for a tomb or catacombs, competing with the Thieves' Guild, smuggling arms into the city, spying on foreign officials, helping an orphan fight against cruel thugs, racing another party in a city-wide search for a magical artifact, investigating a corrupt church, wooing a noble lady, searching for your weapons instructor who has been abducted by a rival, trying to get apprenticed to a truly weird mage, etc.