Hang Son Doong is the biggest mountain river cave in the world; it is so huge that you can fit an airbus A380 and a 40 floor skyscraper inside of it.
The cave is located on the border shared between Vietnam and Laos. Although it was discovered in 1990, the first visit to the cave was organized in 2009.
The cave attracts so many tourists that the waiting list seems endless; the hang son doong can only be visited by 500 persons per year so the ecosystem can be protected.
The visit lasts 5 days and costs 3000 dollars per person.
If you think that you have the guts to try this adventure you just have to wait a year for a spot in the 2018 expeditions.