Waterfall in a Ravine

What would happen if there was more intelligent life than humans, right under our feet? In this world, magical beings otherwise known as Otherkinds, are living underneath you in a city of crystals. However, they are on the brink of attack by creatures brighter, and flashier than.. something bright and flashy. A mysterious prophecy, two kids, and a 8 ball that's an egg. Yeah.