This is a little more generic, but covers a lot of ground in its short five minutes.
The Mound Builders:
Then there is this whole huge culture that absolutely flabbergasted me when I first learned of them a number of years ago. They are the Cahokia. I wish we knew more about them, and what happened to them, but it is a great mystery.
The Cahokia Mounds:
Lastly, there is the fascinating Serpent Mound in Ohio.
Did you know about these cultures? Did any of it surprise you?