The industrial district of Locastus, where huge, cathedral-like factories rise over the low brick houses, and tall ivy-choked chimneys spew out black smoke, day and night.
You receive a vision of a rooftop "somewhere close by", where a rare moss grows; in the vision, you know the moss is suitable for greatly enhancing the effects of certain types of potions. Now go and find that rooftop. Don't fall off. (Of course, rooftop runners *will* be taken for miscreants by the local City Watch....)