The experience of Carlsbad Caverns in New Mexico begins with a leisurely stroll down a paved path that descends over a mile from daylight into the perpetual night of one of most spectacular publicly accessible caverns in the world.
I’ve been there three times now, the first as a child of 10, the second when I took my son near the same age, and the third on my own as an adult, with a camera. Over those ~50 years of visits, nothing has changed: not the long entry, the astonishing geologic features, not even the Lunch Room at the lowest chamber of public use, and its boxed lunches! Also, that long descent every time resulted in shin splints, so some visitors might be glad to know of the elevators from the above-ground visitors center down to the Lunch Room from where it’s possible to explore the more level lower chambers and sights.
One of the most popular features of a visit to Carlsbad Caverns is the evening bat-flight, as hundreds of thousands of bats emerge through the cave’s natural entrance for their night’s foraging.
(Wikipedia has a very informative article about Carlsbad Caverns National Park of which the Caverns themselves are only a part.)