The Forgotten City

This is a bit lengthy. First you need to speak to Vergil, one of the merchants, and he'll talk about being harassed by an unknown person. Once the quest is active you can talk to a few different people and eventually figure out who is causing the problem.

First need to acquire the Golden Bow. You get the bow as part of a quest from Desius. It's actually the quest to get the bow that allows you to progress forward with this achievement.