You want to see a salt mine, they have massive underground salt mines in Kansas. I don’t know if they are this big, but I imagine you could arrange a tour for a lot fewer $$.
Age of the salt deposit, in years. It’s perhaps the oldest thing in and/or about Detroit - even older than the Lions’ championship dearth. Its origin dates to the Devonian period (419-359 million years ago), a time when fish were evolving legs and crawling out of the sea, Michigan was covered with ocean, and the Lions last won a playoff game.
https://www.mlive.com/entertainment/2017/07/detroit_salt_mines_inside_mich.html