- Travel to Nashkel and make your way towards the south bridge.
- Speak with Edwin, accept his offer to find and kill a witch, and allow him to join your party
- Travel to the Knoll Stronghold in the south west of the world map
- Cross the bridge and ascend the stairs to enter the stronghold
- Ascend a second set of stairs and start heading east
- You will have to fight through a group of 15+ knolls
- On the farthest east is a pit that contains Dynaheir (around 2470, 1400)
- Speak with her and choose to complete Edwins deal (killing her).
- Kill her in the fight, speak with Edwin, and the achievement is yours.
Note: This achievement has a companion which will be impossible to obtain without a save reload.