Earth is experiencing ever-increasing waves of earthquakes, tornadoes, and volcanic eruptions. Nobody can figure out why, until three normal kids discover a mysterious metal door in the woods. When they find strange footprints outside the door, and a curious note attached to it, the children start their journey into the mysterious depths of the planet, learning that there may be a little more to the planet's inner workings than meets the eye.This easy-to-read middle-grade book is a great way to open a child's imagination about space and encourage them to explore the universe's endless possibilities. With a 10-year-old female protagonist, the book promotes gender equality and sends a strong message that girls can do anything they put their minds to.