Beneath our feet lies a hidden world of passageways carved through rock, soil, and even under oceans. This book takes curious kids on an exciting journey into that underground world, showing how people throughout history—and even animals—have created tunnels for travel, safety, and discovery. From ancient hand-dug aqueducts to modern tunnel-boring machines the size of skyscrapers, readers will uncover the creativity and courage it takes to solve some of the world’s biggest challenges by digging below the surface. Along the way, kids will meet the tunnels that carry trains, cars, and subways through mountains and under cities, as well as the ones that move water, power, and internet cables. They’ll see how animals like ants, moles, and prairie dogs inspire human engineers, and how teamwork and problem-solving turn impossible obstacles into pathways that connect people and places. Each chapter brings the underground to life with stories of dramatic builds, fascinating challenges, and the people who dared to think big enough to tunnel through them. Perfect for readers who love science, history, and adventure, this book shows that tunnels aren’t just dark, hidden spaces—they’re proof of what humans can achieve when creativity, teamwork, and determination come together to solve enormous problems.