According to VietKings, Vietnam will ask WorldKings to recognise Son Doong Cave as the largest natural cave in the world. 

Son Doong is located in Phong Nha-Ke Bang National Park in Son Trach commune, Bo Trach district in the central province. The cave was formed between 2 and 5 million years ago. 

Son Doong Cave is more than 200m high, 150m wide and approximately 5 to 6.5 km long. 

Within its caverns lie a jungle and a river. The cave is large enough to fit a 40-storey skyscraper inside. The cave was classified as the largest in the world by the British Cave Research Association.