Natural Facts: Nobody is sure what causes the sailing stones or volcanic lightning. Also, the glowing waves are causes by phytoplankton, and the fire rainbows are made from ice crystals instead of water droplets.
Explore the ancient caves of Hang Son Doong, Vietnam. Hang Son Doong is one of the largest caves in the world and features a fast-flowing underground river. For spelunkers, exploring Hang Son Doong is the equivalent of scaling Mount Everest.