Detroit's salt mine: City beneath the city
The Detroit News
Men work in the salt mine underneath Detroit in this undated photo. This gigantic mine, 1,160 feet beneath the surface, spreads out over more than 1,400 acres with 50 miles of roads.
https://www.detroitnews.com/picture-gallery/news/local/michigan-history/2020/01/26/detroit-salt-mine-city-beneath-city/4523991002/