Wow. Ryan Deboodt took a drone inside Hang Son Doong in Vietnam, also known as the world's largest cave, and captured stunning footage that shows off a world that looks like no other. You get a sense of the size of the place—the biggest chamber is 3.1 miles long, 660 feet high and 490 feet wide—and you feel its beauty.
Fantasy and sci-fi are replete with underground cities: Ember, Zion, Menzoberranzan, Khazad-dûm and more. But are there any caves on Earth that are large enough to actually contain a real, functional city?