Today's tunnels, which extend through mountains and underneath oceans and rivers, are marvels of engineering. Readers take a close-up look at these structures and how they are built and maintained. Each chapter will focus on a key area, including the earliest tunnels, the technological advances that have improved their design and construction over time, profiles of tunnel-related careers, and examples of the most impressive tunnels in the world. This book's content correlates with Next Generation Science Standards, ensuring that young readers gain a deeper appreciation and respect for tunnels and the workers that create and maintain them.