Sentence examples for an underground topic from inspiring English sources

It's kind of an underground topic".

Or about an underground city.

She ran an underground charity.

"It's an underground scene".

I am an underground formal person.

-- an underground opposition group.

Does Jerusalem, I asked, have an underground?

That's an underground scene, but still".

Dig an underground parking garage.

It was an underground mining.

Oh, and an underground tennis court.