Deep under Manhattan is the largest construction project in city history. So far, the project has taken the lives of 23 workers, or "a man a mile."

A Nesting Doll of Churches.

The largest of London's subterranean rivers and once a mad, bad center of London life.

Stockholm's decidedly unique public transit system has doubled as the world's longest art gallery for decades.

The internet as provided by a James Bond villain.

Jesus' footprints and the first catacombs in the world.

The world's largest drain sits below the city of Kasukabe, Japan.

A marvel of Byzantine engineering under the streets of Istanbul.

The underground sanctuary of a mysterious ancient cult.

A beautiful and abandoned New York subway station from 1904, complete with chandelier.

One of the largest underground systems runs under Canada's largest urban center.

Beijing's expansive subterranean hiding spot now crumbles away as a tourist destination.

Montreal's colorful subway station shows its support of the local LGBT+ community.