Just something to aid in setting the scene on some secluded back alley. Can also be used to pull off dingy maintenance corridors and whatnot to some extent.
As for triggers, word alley tends to get a wider back alley and narrow alley more narrow one. Add to them other descriptive words like clutter, city, building, street, bicycle, outdoors, trash can, car, air conditioner, night, day, tree, plant, industrial pipe, power lines, cable, light, street lamp, sign, graffiti, poster, and so on...