Detroit has always been a city of layers. Above ground, its towers, factories and neighborhoods tell the story most people know. Beneath the streets is another world: a vast salt mine, utility tunnels, old transportation corridors and stories that sit somewhere between engineering record and urban legend.
A city built above another world
Detroit’s underground story begins with geology. Hundreds of millions of years ago, an ancient sea covered this region and left behind enormous salt deposits. Today, the Detroit salt mine stretches beneath the city in a network of broad corridors carved deep below the surface. Equipment has to be lowered underground in pieces and reassembled, creating an industrial landscape few Detroiters will ever see.
But the salt mine is only one part of the story. Beneath downtown are utility passages, steam tunnels and service corridors built to keep a growing city moving. Some are documented. Others survive through photographs, workers’ memories and stories passed from one generation to the next.
Tunnels, infrastructure and legend
Every old city collects tunnel stories. Detroit is no exception. Tales connect hotels, theaters, factories, riverfront buildings and Prohibition-era speakeasies. Some routes had practical purposes: moving utilities, freight, workers or supplies out of sight. Others have been exaggerated over time. The fascination comes from separating what is physically there from what Detroit has imagined beneath itself.
Watch the full story Friday at 5:55 PM
Our new History Loves Company documentary explores the salt mine, historic tunnels, forgotten infrastructure and the legends that have grown around them. It is a journey into the parts of Detroit that most of us pass over every day without realizing they exist.
Premiere: Friday, October 16, 2026 at 5:55 PM ET
Every home has a story. Every street has one too. Sometimes, the story is directly under our feet.
