I believe it’s Mamouth Cave in TN. Never been there, but I did tour Lewis and Clark cavern as a kid. Very impressive.
I have been to Mammoth Cave and it is impressive. Actually, I looked at pictures at the front but did not pay to go in, but rather went to a rear entrance for research on a historical novel I am doing. Of course, Virginia and West Virginia have a number of interesting and picturesque caves.
I am wondering if archeologists will be allowed to search for possible ancient remains in this and other Vietnamese caves.