Mammoth Cave National Park is home to the world's longest known cave system.
The Great Smoky Mountains National Park is a vast area of pristine wilderness, spanning more than half a million acres.
Cahokia Mounds State Historic Site is home to a prehistoric Native American city near Collinsville, Illinois.
Poverty Point is a historic archaeological site that features various earthwork constructions.
Independence Hall is the building where both the United States Declaration of Independence and the United States Constitution were debated and adopted.
Liberty Island is home to the Statue of Liberty.