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Chicago has a disused freight tunnel system larger than either of these pedestrian tunnel systems: https://en.wikipedia.org/wiki/Chicago_Tunnel_Company https:/

• fencepost 9y ago
  Which many Chicagoans learned about when someone drove pilings into it allowing the river to drain into the tunnels. It was huge business news at the time, because basically all of downtown Chicago was shut down for a week or more since power, etc is delivered to the buildings through those flooded basements. https://en.m.wikipedia.org/wiki/Chicago_flood https://en.m.wikipedia.org/wiki/Chicago_flood