Have you ever seen a forest side of a cave? When I first watched this video, I kept wondering, "Ok, when are they going to show the cave?" before realizing that we were already inside the cave!
The cave is called Hang Son Doong, and is located in Vietnam. Discovered in 1991, this film does a seriously fantastic job at showing just how massive and mysterious a structure this is. And this only shows a small bit of the cave. The video was filmed near the entrance and at the first and second dolines (skylights) which are 2.5 and 3.5 km inside the cave respectively.
How did it form?
It's believed the cave was formed between two and five million years ago. River water from the mountain river (that's what the name Son Doong means: mountain river) may have eroded the limestone beneath the mountain. This led to the incredibly high ceilings and unique cave. Hang Son Doong is 200 meters wide, 150 meters high, and 9 kilometers long. Just imagine a 40 story building inside a cave, and that's what we're talking about.
While the most common, safe tours of this cave cost upwards of $3,000 USD, I need to go! You have to be kind of physically fit to do this, but I think it's worth the money and the effort to see this magnificent site in person!