- Go to the "Area South of Lighthouse" (Archaeological Site)
- North East of the Center is a digsite. Talk with Charleston Nib and accept his offer to guard the site.
- Speak with Gallor, if he doesn't speak to you. Refuse his request to kill Charleston
- Speak with Charleston again, a short cutscene should play
- Kill all the "Diggers"
- Talk with Charleston one last time and the achievement is yours.
Note: The companion to this achievement will be unobtainable without a save reload.
This achievement can be done immediately afterwords if you have the idol.