Did you know there’s a hidden world below the streets of Detroit? Roughly 1,100 feet down sits a massive salt mine stretching over 1,500 acres with more than 100 miles of tunnels. A full-blown city beneath the city. And it’s still in use today. It all started 400 million years ago, when a prehistoric sea dried up and left a thick bed of salt buried deep beneath Michigan. In 1895, drillers hit rock salt. By 1906, the first shaft was underway. The work was brutal. Explosive gas, extreme heat, and