A 235-step spiral staircase leads into this vast cavern. More adventurous sorts can rappel into the chamber—ropes and instruction are provided. Otherwise, the only way inside is via the 45-minute tour, during which you'll see giant (and still growing) stalactites and stalagmites and an archaeological site that holds some of the oldest human remains yet found in America (an unlucky person has fallen into the cavern about once every 130 years for the last 13,000 years).
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