Hang Son Doong Cave – Located in Phong Nha-Kẻ Bàng National Park, Quảng Bình Province, Vietnam (near Laos-Vietnam border). It has a great fast-flowing underground river inside. Sơn Đoòng is a Vietnamese word meaning “Mountain River Cave” . A British caver walks through Vietnam’s Son Doong cave; Earth’s biggest recognized cave passage. It was discovered in 1991, and it became publicly open in 2009 after group of British scientists conducted a survey. Son Doong Cave surely is the biggest cave in Vietnam which is five times bigger than Phong Nha Cave (Previously biggest cave in Vietnam).