Ban Gioc Falls (Thác Bản Giốc) is a waterfall on the Quây Sơn River, which the Chinese call the Guichun, exactly where the river forms the border between Vietnam and China. It lies in Đàm Thủy commune of Cao Bằng Province, about 272 km (169 mi) north of Hanoi, opposite Daxin County in Guangxi, where the Chinese half is called Detian Falls. The river drops about 30 m (98 ft) across a front roughly 300 m (980 ft) wide, splitting into separate falls in the dry months and joining into one sheet after heavy summer rain. It is often counted as the fourth-largest waterfall on an international border, after Iguazu, Victoria and Niagara, and it sits inside the Non Nước Cao Bằng UNESCO Global Geopark, which covers about 3,000 km² and was listed in 2018. This guide follows the river itself: from its source in the Guangxi hills, down the border line, over the limestone step, and on into the cave country below.
Jingxi County and the Chongshan Hills: Where the Quây Sơn Begins
The Quây Sơn rises in China, in Jingxi County of Guangxi, among the steep hills Chinese sources call the Chongshan range. It starts as one of many small karst streams. This is mature karst, where the original limestone beds have been worn down for millions of years and water travels as much underground as on the surface. Lower down, around the falls themselves, numerous streams spring from underground fissures in the limestone, so the river is fed by groundwater as well as by rain.
From Jingxi the river passes into Vietnam's Cao Bằng Province, and for part of its length it runs along the border itself. On the Vietnamese side, the high ground around Trà Lĩnh holds Thang Hen, a group of 36 natural lakes sitting on a hilltop at about 1,000 m (3,300 ft). Their water level rises and falls like a small tide, which is put down to artesian springs pushing up through the limestone. Some of the lakes drain out as streams that eventually reach the river feeding Bản Giốc. Also in Trà Lĩnh is the "Eye of God" mountain (Núi Mắt Thần), one of the best-known sights of the geopark.
Along the Border Line: The 1887 Convention and the 1999 Treaty
For part of its course the Quây Sơn is the international boundary itself. The legal line between Daxin County and Cao Bằng follows the midline of the watercourse. That line goes back to the Sino-French border commissions that followed the Treaty of Tientsin of 1885. They worked from late 1885 to 1887, and a convention signed in Beijing on 26 June 1887 fixed the frontier between Tonkin and Qing China. A second convention in 1895 settled some disputed sections, and between 285 and 341 markers were put up. The markers were not tied to a coordinate grid, many were later lost or moved, and the old maps were often vague. That left the border between Vietnam and China, now 1,297 km long, open to argument.
Those arguments came to a head in the 1970s and in the war of February 1979. On 27 February 1979, Chinese troops occupied Cao Bằng city, and the area around the falls was one of the crossing points for the Chinese army. After relations were normalised in 1991, the two governments signed a land border treaty on 30 December 1999. It split roughly 227 km² of disputed land almost evenly, 114 km² to China and 113 km² to Vietnam, and marking on the ground was finished in 2008. Talks on the stretch at the falls went on until at least 2009. The agreed principle is that the border follows the median of the main flow. A stone marker inscribed in French and Chinese stands beside a road above the falls. Some Vietnamese commentators argue that it was moved during or after 1979 and that the whole waterfall should be Vietnamese. The treaty line is the one both governments apply; the claim is still voiced by some in Vietnam. The rest of Vietnam's land frontier is mapped out in our post on the countries that border Vietnam.
The 30-Metre Drop at Đàm Thủy: Thác Chính and Thác Phụ
The falls form where the river crosses a series of limestone steps. The water does not drop over a single cliff. It steps down from one bedrock layer to the next, and each step marks a different layer of sediment laid down over millions of years. Harder beds hold the ledges and softer ones are cut back beneath them. The same erosion is slowly pushing the crest upstream. Over thousands of years the lip has retreated, and in doing so it split one waterfall into the two that most visitors see.
In Vietnamese the two are treated as parts of a single fall named Bản Giốc: thác chính, the main waterfall, and thác phụ, the subordinate one. Chinese texts tend to call the whole system Detian, and they sometimes name the smaller section Banyue. Rocks and trees break the main front into three falls, and the noise of water striking the cliffs carries a long way down the valley. When summer rain swells the river, the gaps fill and the falls run as one wide curtain again. The Chinese approach, from Daxin County in Guangxi, is described in our separate post on Detian Falls.
People came here for more than the view. In the 1920s the French used the falls for hunting and fishing and built cottages beside them, and the river is known locally for a fish called "tram huong". Today tourism is the main business of the area. The village sits in what was until 2025 the district of Trùng Khánh, which had 70,424 people across 688 km² in 2020 and is best known in Vietnam for its chestnuts. Vietnam abolished its district tier on 1 July 2025, and Cao Bằng is now divided directly into 56 commune-level units.
Ngườm Ngao, the Tiger Cave, a Few Kilometres Downstream
Downstream of the falls, the river's underground side comes into view. Ngườm Ngao Cave lies in Bản Gun village of Đàm Thủy commune, about 3 to 5 km from the waterfall. In the Tày language ngườm means cave and ngao means tiger, so the name translates as "Tiger Cave". French and Vietnamese officials found it in 1921 while they were visiting Bản Giốc. It was surveyed in 1995 and opened to tourists in 1996.
The cave runs for 2,144 m and has three main entrances. Inside, the temperature stays between about 18 and 25°C, and streams still run through parts of it. Its formations have names taken from local life: the inverted lotus platform, the silver and golden trees, dragon boats, terraced rice fields and the four heavenly pillars. Lit walkways cover about 2 km. Ngườm Ngao shows the same process that built the falls, working inside the rock. Acidic water dissolves the limestone along its joints, then leaves calcite behind as it drips. Our guide to karst landscapes explains how one rock produces both towers and caves.
Farther afield on the Chinese side is Tongling Gorge, in Baise in Guangxi. It is about 1,000 m long and 200 m wide and can be reached only through a cavern from the next gorge. It was rediscovered only recently and has plants found nowhere else. Gorges sealed off by rock walls like this one are where such isolated plant communities survive.
Below the Falls: Rice Terraces, Tày Villages and the Geopark Calendar
Around Bản Giốc the river runs between flat-floored paddies hemmed in by limestone hills. Cao Bằng is overwhelmingly rural. In 2019, 406,934 of its 530,341 people lived in the countryside, and the province had about 547,849 people by 2023 over 6,700 km². The Tày and Nùng, upland Tai-speaking peoples, make up about 70% of the province's population, as the chart above shows. The Kinh majority of lowland Vietnam is a small minority here.
The river sets the calendar. From August to October the water is at its highest and the falls run white, just as the terraced rice fields turn gold for harvest. From October the flow drops and the water becomes calmer and clearer. November and December bring wild sunflowers and buckwheat in bloom, and pear blossom follows in March. Summer rain gives the biggest single curtain of water. The months after the rains are when the falls and the farmland look their best together.
Reaching the falls is part of the trip. Cao Bằng city, the provincial capital, stands where the Bằng Giang and Hiến rivers meet at about 300 m above sea level. It sits on Highway 3, some 270 km from Hanoi, and the road north from Thái Nguyên climbs through the Cao Bắc Pass. From the city the falls are another 80 km (50 mi) north through the karst. The geopark's 2018 listing ties this whole route together: the lakes on the plateau, the cave, the border river and the falls. It gives the province a reason to protect the river along its full length, not just at the drop that appears on the postcards.
The trip from source to plunge pool covers both sides of a border that took more than a century to settle. Rivers drop over rock on this scale in plenty of other places, and the countries with the most waterfalls are ranked in a separate post.