Ĉe la koro de la tero

An enterprising inventor and his young companion build a tunneling machine and break through into a vast hollow world at the planet's center, lit by a tiny central sun and populated by prehistoric animals and diverse human cultures. They confront an intelligent reptilian race that dominates the inhabitants and, through alliance-building, daring rescues and pitched battles, work to free and uplift the captive peoples while surviving natural and social hazards. The narrative pairs fast-paced adventure and escapes with recurring motifs of exploration, technological ingenuity clashing with primal forces, and the ethical tensions of bringing external civilization to isolated societies.