Yellowstone National Park was the first national park — and that's just the first in a string of superlatives that come to mind: the world’s largest concentration of geysers, the largest lake above 7,000 feet in North America, the largest concentration of mammals in the lower 48. The park straddles Wyoming, Montana and Idaho, and offers a wide diversity of landscapes that — amazingly — you can actually see in one day ... if you plan your day correctly. Long story short, you should add a visit to the home of Old Faithful to your to-do list.