7.) Grand Canyon | Arizona, United States
Thank the Colorado River for carving the steeps sides of the Grand Canyon. Recent findings suggest that the river first made it’s way through the canyon 17 million years ago. As the water level lowered more and more of Earth’s geological history has been exposed–nearly two billion years of it. Why visit a hole in the Earth? Because you can see it from space.
(Image Source: Flickr | Airwolfhound)