Nguom Ngao Cave

Cool, damp air drifts out of the cave mouth, and with it comes the sound of running water. An underground stream flows deep inside the rock, and the stone walls throw it back like the roar of a large animal. The Tày who lived here long ago called this place Ngườm Ngao, which means Tiger Cave. That is the local explanation of the name. The Tày are one of the peoples of northern Vietnam.

The cave lies in Đàm Thủy commune. That is in the Trùng Khánh area of Cao Bằng province. The city of Cao Bằng is about 90 kilometers away, and Bản Giốc Waterfall is almost 4 kilometers away.

The story of the cave begins very far back, in the most literal sense. The cave grew in limestone that holds fossils of coral and sea lilies. That rock formed in an ancient sea about 400 million years ago, when this land was a seabed. Coral and other sea creatures died and piled up, layer on layer, until they became limestone. Tens of millions of years later, the land was lifted into mountains. Then rainwater, made weakly acid by the air, seeped into the limestone and widened every crack, until a system of underground caves had formed. Over millions of years more, dripping water carried calcium into the caves and left it behind. The calcium hardened into the shapes that fill the cave today.

The Cao Bằng tourism portal reports a survey from 2016 that measured the cave at 2,769.6 meters long. It is 61.1 meters deep, with two levels of passages and five entrances. The active level lies at the height of the stream. The fossil level sits about 50 meters higher. The usual route through the cave covers 945.8 meters, and that stretch is open to visitors and lit.

Inside, stalactites hang from the ceiling and stalagmites rise from the floor. Given enough time, the two meet and become stone columns. The province's own tourism pages name several shapes in the cave. The names of these shapes include the golden waterfall, the silver waterfall, the upside-down lotus, the lone stone pillar and the terraced fields. Two people looking at the same mass of rock can see two different shapes, and that is perfectly natural.

Beneath the cave runs an underground stream, over a bed of pebbles and gravel. Its water flows out toward the Quây Sơn River, the same river that forms Bản Giốc Waterfall. So the cave and the waterfall are linked through the groundwater and surface water of the Cao Bằng karst.

There is also a route called Ngườm Ngao and Bản Thuôn, which opened on April 29, 2021. The tourism portal describes dark stretches of cave, climbing, wading, and kayaking inside the mountain. The route leads deep into a limestone mountain that is millions of years old.

The cave is part of the Non Nước Cao Bằng UNESCO Global Geopark. A UNESCO Global Geopark is an area with landscapes of international geological importance, managed for protection, education and sustainable development. Every stalactite and every column in the cave is the work of water dripping patiently over a very long time. These shapes have been here longer than any civilization on Earth.

Daylight floods in at the cave mouth after the cool dark under the mountain, and the feeling stays of having stood inside stone that the earth took 400 million years to make.