Hut Wrecker Achievement
Chapter 12 - Destroy 3 enemy huts with boulders Giants can lift
At two points during this stage, you'll have fights where enemies spawn from out of a nearby hut. Switch to a Giant Skylander, pull up one of the boulders in the area, and toss it at the hut to destroy it (preventing any more enemies from spawning there).
The first hut is near the start of the chapter, in front of the first gate. The second and third huts are later in the stage, just before you enter the Crystalsong Mines. There is one on each side of the entrance to the mines.
Here is a video by 2-4 Gamerz showing the locations: