Thousands of years ago, ancient engineers came up with a way to cross obstacles that prevented people getting from one place to another. They built a passageway under the ground called a tunnel. A tunnel sounds simple. After all, it is just a tube built through dirt or stone. But building a tunnel is one of the hardest challenges an engineer can face. This scientific text highlights the origin of the first tunnels, the greatest tunnel builders, the evolution and advancement of tunnels that are being built today, and the complex wonders they are! This title will allow students to recognize how engineers improve existing technologies or develop new ones to increase their benefits, decrease known risks, and meet societal demands.