This place is a trail inside a cave in a national park in the United States. It belongs to karst topography, so when walking inside you could see a lot of wonderful scenes. It is so narrow that fat men would have great difficulty in passing through it. If you have been there, you would have an unforgettable memory. Do you know in what national park is it?
It is in Mammoth Cave National Park.
Postscript: The picture is downloaded from the following website:
https://stpaulsbasketball.wordpress.com/tag/stalagmites/