- 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.
- It doesn't matter if you protect Chareleston or bid Gallor's will - make sure you have looted the Idol. (I believe if Charleston is alive and you speak to him with the idol in your inventory he will take it, so talk to him before taking the idol)
- When you leave the tomb with the idol you will be attacked by the Doomsayer.
- The Doomsayer is immune to physical attacks - I completed this by attacking with wands of magical missles and other wizard spells that do typed damage (such as ice/cold)
- When you defeat the Doomsayer you will be awarded 4000xp and the achievement.
Note: There are companions to this achievement which at least one of them can be done at the same time.