Modern science cannot speak with justifiable authority about more than only a tiny fraction of the Earth's interior. We have, literally, scratched just the surface of our planet. Can we know what lies beneath our feet in the unimaginable depths of the Earth? Can spiritual investigation give us answers to our questions about something virtually impossible to perceive through our physical senses?

Rudolf Steiner's discussions of the subterranean spheres are gathered, along with notes and an introduction, for the first time in this comprehensive volume. His unique overview pictures of the...