What is inside the largest cave of the world ?

The Hang Son Doong cave is a 3-million-year-old biggest cave in the world. It is so big it has its own river, jungle and climate. The cave is big enough to fit an entire New York City block with 40-story skyscrapers.
Hang Son Doong is located within the Phong Nha-Ke Bang National Park, it was designated a UNESCO World Heritage Site in 2003.
Oxalis Adventure Tours has mentioned that because of protection and conservation matters, the company can only organize tours for 500 to 600 people during the period from January to August .
The tickets are offered to the first candidates who meet all of the health requirements, as the six-day trips require travelers to be able to trek approximately 50 kilometers, and navigate through the caves. The cave has only been open to tourists since 2013 and according to Company, fewer people have seen inside of the cave than have surpassed Everest. This tour cost US$3000 per person.
Australian photographer John Spies, 59, spent a week photographing the natural wonder of the cave system. “With ceilings towering over 200 metres high in places, the cave is a humbling and belittling experience,” said John, who has lived in Thailand since 1977 and runs the Cave Lodge guesthouse.