A tunnel is a long, narrow passageway that has been excavated through a hill or mountain to provide a route for transportation, water supply, or other purposes. It can also refer to an underground structure built for similar reasons.
Usage examples
Construction: The workers excavated a tunnel to connect two buildings underground.
Transportation: The train passed through a long tunnel in the mountain, allowing for a shorter and safer route.
Mining: Miners used tunnels to extract valuable resources from deep within the Earth.
Exploration: The adventurers ventured into a dark tunnel, eager to discover the secrets hidden inside.
Escape: The prisoners dug a tunnel under the prison walls, hoping to gain their freedom.
Urban: Pedestrians can walk through a tunnel that goes underneath the busy street, ensuring their safety.
Sports: The athletes ran through a specially designed tunnel, cheered on by the roaring crowd.
Military: Troops used underground tunnels to move undetected and surprise the enemy during battles.
Hydroelectricity: Water flowed through a tunnel to power the turbines, generating electricity.
Communication: Fiber optic cables were installed in a tunnel to provide fast and reliable internet connection.
And I have a kind of tunnel vision from inside my helmet. (si.com)
It is just too difficult to find weapons hidden in tunnels in the mountains. (politics.stackexchange.com)
Model jet fighters and even space shuttle prototypes have been painted with this stuff and tested in wind tunnels in an effort to make them fly better. (scientificamerican.com)