Yellowstone National Park
The natural wonders of Yellowstone National Park draw over 4 million visitors per year. The geysers are the main draw, followed closely by the colorful hot springs, but the pristine plains filled with American buffalo awe visitors in near equal measure, harkening back to a time before the closing of the frontier.
While geysers like Old Faithful are the main draws, most visitors will find their time in Yellowstone walking around the massive hot springs.
Even if you think these walks aren't for you, don't dismiss them out of hand. The deep abyss of Morning Glory has a way of pulling even the deepest skeptics into a trance.
And the colors of Grand Prismatic Spring will dazzle you too.
While it is possible to see many of Yellowstone's great sights in one day, most visitors will stay longer. Excellent suggested itineraries can be found on the site "Secret Yellowstone."
If you have the time, you should also check out the adjacent Grand Teton National Park.