Hang Son Doong in the Phong Nha-Ke Bang National Park in central Vietnam is the largest known cave in the world. To experience Bhutan's beauty, one needs to be prepared to do a lot of walking.
Caption: 
World's largest cave in Vietnam: Hang Son Doong in the Phong Nha-Ke Bang National Park in central Vietnam is the largest known cave in the world.
Credits: 
PHOTO: AVESON TRAVEL; ELINNA YAO; GLENN YONG, COCOTINOS MANADO; JNTO; LINDBLAD EXPEDITIONS; TERTIUS GOUS