Many Vietnamese fans thanked Garrix for coming to Son Doong Cave and invited international friends to visit Vietnam. Son Doong Cave was discovered in 1991 by a local man named Ho Khanh. Son Doong Cave is nearly nine kilometers long with sections reaching up to 200 meters tall and 160 meters wide. Photo: Instagram of Martin GarrixIts name Son Doong means the ‘cave of the mountain river’ or ‘cave of mountains behind Doong [Village].' Photo: Instagram of Martin GarrixSon Doong Cave is five times larger than Deer Cave in Malaysia, the world’s largest known cave before Son Doong was found.