phong nha ke national park / vietnam, 16/11/2017: group ziplining over an underground river inside the giant hang tien cave in the

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