I smile at our guide's warning and enter the lush jungle growing inside Hang Son Doong, a three-million-year-old cave in central Vietnam. The expedition to Hang Son DoongCampsite in the cave: Hang Son Doong expeditions are physically demanding. In 2013 Hang Son Doong was opened to the public for the first time, with the adventure tour company Oxalis running the exclusive five-day expedition. The eco-system inside Hang Son Doong is as unique as it is large, and it even has its own localized weather system. As one of the last truly pristine environments in the region, Hang Son Doong is a place so remarkable that it demands protection.

Source: CNN September 05, 2016 00:56 UTC