Your familiarity with cities tells you what will support your weight and helps you perceive things that are out of place.

Daily
Free Action      Personal

Trigger: You would make an Acrobatics, an Athletics, or a Perception check in an urban environment

Effect: You make a Streetwise check in place of the Acrobatics, Athletics, or Perception check.

Published in Player's Handbook 3, page(s) 176.