Some 1,200 feet beneath the streets of Detroit, under the north end of Allen Park, Dearborn's Rouge complex, and most of Melvindale runs 50 miles of subterranean roads over an area of more then 5.6 kilometers. It is the Detroit Salt Mine, and as a Detroit industry it is older then automobiles. As a geological entity, this salt deposit is older even than the dinosaurs.
The coords are the entrance to the mine.