Just south of Rapid City. The location doesn't transfer any more to Google Maps. Pooey! Doesn't matter, I just did this because it is such a great tourist spot. Did the trip a thousand years ago when I took the sister's car from LA to Chicago. The Wind Caves, or Whistling Cave is fantastic for a geophysicist. It is such a huge volume that only exits at a small spot, so it was discovered by the steam whistle effect when the barometer changed. They are still exploring it.