The Berkeley Pit, in Butte, Montana, was once the richest hill on Earth: the Anaconda Copper Mine. Now: it's not all that rich, and it's not much of a hill. Instead, it's a toxic pit filled with sulfuric acid. Thanks to the Montana Resources team: https://www.montanaresources.com/ REFERENCES AND FURTHER READING: "10,000 miles of tunnels": https://mtstandard.com/news/local/new-map-plots-butte-underground/article_f1de51e2-948f-5634-9aa0-87ad730d9cfd.html "35,000 people a year": https://www.travelandleisure.com/trip-ideas/toxic-montana-pit-tourist-attraction] Protective Water Level, and the details of the underground water that I didn't have time to go into: https://pitwatch.org/protective-water-level/ The first treated water being removed from the pit: https://www.mtpr.org/post/treated-water-begins-flowing-out-buttes-berkeley-pit Edited by Tom Fuller I'm at https://tomscott.com on Twitter at https://twitter.com/tomscott on Facebook at https://facebook.com/tomscott and on Instagram as tomscottgo