Missouri · (MO)
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modern house inside a cave.. http://inhabitat.com/6-fascinating-underground-homes-that-go-above-and-beyond/2/
Greer Spring, Mark Twain National Forest in Missouri. There is a mile long trail that heads down to the spring. Greer Spring is the second largest spring in the Ozarks, and in Missouri. 222 million gallons of water bubble up from the spring, and then flow into the nearby Eleven Point National Scenic River.