Son Doong Cave is a natural wonder that should be on everyone's bucket list. Discovered in 1991 by a local man, this cave is the largest in the world, with caverns large enough to fit an entire city inside them. The cave is also home to some of the most unusual geological formations you'll ever see, including a river that flows through a towering mountain. With its dramatic cliffs, pristine caves and verdant jungle, Son Doong is like something out of a fairy tale.