We somehow missed posting this fascinating video when it first came around.
After several hundred years there’s almost nothing natural about Chicago’s natural environment. Human effort on a massive scale, most of it unseen by almost all of us, keeps us from reverting to a natural environment.
What would happen if that effort ceased is the subject of the video, which was published when we still had a Sears Tower. You can see the series that inspired the video at History.com.