

The underground tunnel was dark and quiet.
Located or happening beneath the surface of the ground.
The underground river flowed swiftly.
They discovered an underground cave.
The city has an extensive underground system.
underground station
underground network
underground parking
subterranean
belowground
buried
I took the underground to get to the city center.
A place or system that is below the surface of the ground, often used for transportation.
The underground is often crowded during rush hour.
We found a nice café near the underground station.
The underground connects many neighborhoods in the city.
underground train
underground station
underground system
subway
metro
tube