The archaeologists dug until they found pottery underground.

Many cities are investing in modern underground railways to reduce traffic congestion and curb carbon emissions.

The city's new underground railway has cut commuters' travel time in half.

Many 19th-century accounts refer to the underground railway as a courageous, covert network that guided enslaved people north to freedom.

The historian's lecture focused on the role of the Underground Railway in helping escaped slaves find freedom.

Historians have documented numerous covert routes of the Underground Railroad that guided fugitive slaves to freedom.

I take the London Underground to work every morning because it's the fastest way across the city.

We cooked underground mutton over the campfire, and despite the name it was just rabbit.

Startled by the hounds, the fox tried to go underground to escape.

Many college radio stations in the 1980s helped spread the Paisley Underground beyond California's borders.