Underwater tunnels are structures built beneath bodies of water, allowing vehicles and trains to travel from one side to the other without needing to go around. These tunnels are often constructed using advanced engineering techniques to ensure safety and durability. They can be made from materials like concrete and steel, designed to withstand water pressure and environmental conditions. One famous example of an underwater tunnel is the Channel Tunnel, which connects England and France beneath the English Channel. Underwater tunnels can also serve as important transportation links, reducing travel time and improving connectivity between regions.