This blocks the Riddlemaster achievement, so be sure to make a separate save before attempting this.
At the start of Chapter 8, go east from the camp. You'll see a bard singing to a stone. You'll need to sing to the six stones in the area (three on either side of the road) and FAIL the charisma check each time. One obelisk has a riddle for you to solve. The correct answer is "The wind blowing in a tree next to a river." (Dynaheir can also guess it for you), but you must give a wrong answer. The stones will spawn a Stone Golem and a wraith, so be prepared to run. Once you fail the last one, the achievement will unlock. If the obelisk lights up after "singing" to it, your character passed the check.