By Kelsey Campbell-Dollaghan

Road salt is one of those city services that we take for granted, an invisible network infrastructure with a murky provenance. But though you may not know it, the salt on your roads might come a sprawling, century-old mine right below your feet.

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Source: http://feeds.gawker.com/~r/gizmodo/full/~3/VJj8kd9f3fs/the-incredible-urban-salt-mines-hiding-underneath-our-f-1516664767