Ran across this video of a quad copter tour of the large sinkhole part of the Hang Son Doong cave in Vietnam. Imagine the size of the room this area made before the roof collapsed! I realized I read the National Geographic article a few years ago, it has better pictures of the interior portions of the cave.
[vimeo=https://vimeo.com/121736043]
National Geographic article(check out the interactive 3D fly through)