Son Doong Cave (Photo: VOV | Hoang Trung)

Son Doong Cave came in fifth behind Mount Kilimanjaro in Tanzania, the Inca Trail leading to Machu Picchu in Peru, the Grand Canyon in the United States, and Thrihnukagigur Volcano in Iceland.

Because the cave is physically challenging, visitors must register  for a guided tour led by an experienced team with specialized equipment.