Midway though the chapter you'll encounter a group of scientists that challenge you to Skystones for a key. To the right of them is a traptanium crystal. Smash that and go across the bridge that forms to find an area with two elemental gates and a pump switch in the center. Jump on the switch and you'll be taken down to the Meditative Pool.
In this pool, there are the 12 golden balls and a waterfall to the south (There's also a Winged Sapphire in the northwest). You need to move the balls off of the waterfall. To do so, you need to gently walk into them to push them away. DO NOT ATTACK THEM; They are basic breakable objects and any attack will destroy them. Similarly, any skylander with an active passive attack, such as Lightning Rod, will accidentally destroy them, so don't use them. Also, be wary of the walls. If you push a ball into a wall too hard, it will shatter.
Each time you push a ball off, a few gems will fall from the ceiling. Push the last ball off, and you'll get a pile of pocket change and the achievement.