http://www.ozarkcave.com/ [1]

"A “luxurious cave” may sound like the ultimate contradiction. This property, built into the Ozark Mountains, features natural rock walls and ceilings as well as Jacuzzi bathtubs and large windows for letting in light. Built as a Cold War bomb shelter by John Hay, founder of Celestial Seasonings tea, it’s now a base from which to hike, bike and explore local springs." - Forbes