go underground

The river goes underground, just past where they were lost.

David told his mother he was going underground for a few days.

Two of their close friends went underground during this period.

Because the very nature of disease has changed since we all went underground.

She was therefore required to go underground with her political work.

He went underground one day and was missing for almost a week.

About half of all sets were taken, the rest went underground.

However, the Project had simply taken advantage of this to go underground.

You'll make it go underground, and that's the last thing you want.

The men are in much better spirits since they went underground.