Hollow Earth Protocol

Hollow Earth Protocol is a gripping science fiction adventure set in a future where humanity discovers a hidden civilization buried deep beneath Earth's crust. When a mysterious signal emerges from the planet's core, a team of explorers descends into an immense underground world filled with ancient technology, towering cities, and secrets older than human history. As they uncover the truth, they realize that the fate of both civilizations may depend on a protocol hidden for millions of years.