While not as long as Mammoth Cave, Carlsbad is larger in terms of volume, and both are World Heritage Sites. The ceilings are often over a hundred feet high, and the Big Room spans over 8 acres, with a mile-long loop to see it. Even after descending 750 feet down the natural entrance, there are still deeper “bottomless” pits below. I was fairly sure I heard faint drumbeats coming up from the darkness, so I asked the rangers. They explained that there were only a few goblins, and that they try to catch them as they’re considered “invasive species”. I finished the hike as quickly as possible and took the elevator up.