A submarine tunnel is an underground passageway that runs beneath a body of water, such as an ocean or a river. These tunnels are constructed to facilitate transportation, allowing vehicles, trains, or pedestrians to travel without the need for ferries or bridges. They are engineered to withstand water pressure and are often lined with concrete or steel for durability. One of the most famous examples of a submarine tunnel is the Channel Tunnel, which connects England and France beneath the English Channel. This tunnel allows high-speed trains to transport passengers and goods efficiently between the two countries, significantly reducing travel time and enhancing connectivity.