Where?

Where is the longest underground river located?

VietNam ( Phong Nha-Kẻ Bàng National Park in Quang Binh province )

This cave is 7729 meters long, contains 14 grottos, with a 13,969 meters long underground river. The scientists have surveyed 44.5 km of grottoes in this cave so far but tourists just penetrate to a distance of 1500 meters. Phong Nha Caves, like most of the caves in this area, has been continuously shaped by the Chay River. The karst formation of Phong Nha-Kẻ Bàng National Park has evolved since the Palaeozoic (some 400 million years ago) and it is a UNESCO World Heritage Site.