phong nha ke national park / vietnam, 16/11/2017: group of cavers passing an underground river and huge rocks inside the giant

16112017 adventure and asia bang beauty black caing cave cavern cavers chamber dark exciting experience exploration explore giant group hang huge inside jungle light mountain national nha nhake outdoor oxalis park passing phong rainforest river rock rocks scramble shadow southeast spectacular stalactite stalagmite thrill tien tour tourism tourist travel trip undergound underground vietnam wall water