tunnels
n. countable A2 Elementary US //ˈtənəɫz// UK //tˈʌnəlz// tun·nels
n. long, narrow passages that go underground or through a mountain. They are used by cars, trains, or people to get from one side to the other.
n. artificial underground passages, typically bored through earth or rock, designed to accommodate transportation or utilities.
The train travels through several long tunnels in the mountains.
Engineers are building new tunnels under the river to reduce the heavy traffic on the city bridges.
The ancient city is connected by a vast network of tunnels that once served as a secret drainage system during the rainy season.
Usage
Often used with the prepositions 'through' or 'under'.