Tunnels are underground passages that allow people, vehicles, or trains to travel from one side to another, often beneath obstacles like mountains or rivers. They can be made for various purposes, such as transportation, mining, or even water supply. Famous examples include the Channel Tunnel connecting England and France and the Gotthard Base Tunnel in Switzerland. Building a tunnel requires careful planning and engineering to ensure safety and stability. Workers use heavy machinery to dig through the earth, and they often face challenges like water seepage or rocky terrain. Tunnels can be straight or curved, depending on the landscape and the intended route.