Big Spring

The number is incomprehensible: 286 million gallons a day flows from this aptly named spring. The resulting pool feels more like a mysterious Game of Thrones location than a mere spot in southern Missouri. It's one of the three largest springs in the US and carries at least 70 tons of dissolved limestone up and out of the caverns below daily. There is good hiking in the lands around the vast pool, as well as camping and a lodge.