15. Crater Lake, Oregon
Crater Lake is a favorite tourist spot, for its striking blue waters. The round crater was formed by the collapse of the Mount Mazama volcano more than 7700 years ago. When it rains or snows, the lake is filled; during summer, the lake dries out a bit. There are two islands in the lake too!
As said, its geographical history spans thousands of years, and today you can swim, snowshoe, ski, hike, and cycle through the rugged mountain terrains. There are also countless activities and thousands of acres to explore; adventure is endless at Carter Lake.