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The Minnesota Iron Range is full of these and they're absolutely beautiful; terrifyingly deep, however.

[1] https://www.youtube.com/watch?v=LAL_d-5FsGQ - Tioga Pit Mine (225' deep)

[2] https://en.wikipedia.org/wiki/Portsmouth_Mine_Pit_Lake (450' deep)

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Stumbled across this one later in my recommended videos that I like even better: https://www.youtube.com/watch?v=NC267JdGN24
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Hah! Not every day my neighborhood gets a shout out on HN. I’ve swam in that pit in the video. Neck deep you can see your toes. Found a couple pipe bombs… definitely gets a lot of attention from bored people.
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