This may or may not be the same topic as the sidebar tells me was created in Jan 2011 and March 2014. The video was uploaded to YouTube on Sept 15, 2022.
I guess I can't just put the video here, so here's the link to it: A new subterranean realm is discovered deep in the caves of Vietnam, in this clip from Season 18, "Secrets of Inner Earth."
It was shared on a forum I'm on, with this comment: "This cave i[n] Viet Nam is 40 stories high and includes a forest and it's own eco system."
I immediately though of Mind Reach.