Detian is the largest transboundary waterfall in Asia and the fourth largest in the world along a national border — a fact that becomes more interesting when you consider what that border is. The waterfall straddles China and Vietnam: stand at the viewing area on the Chinese side and you are looking across the cascade at Vietnamese territory. On the Vietnamese side, it is known as Ban Gioc. A bamboo raft ride to the base of the falls will bring you close enough to feel the spray and, if you lean over, technically enter Vietnamese airspace.
The waterfall itself drops about 75 metres over a series of broad limestone shelves, spanning roughly 200 metres at its widest. In the rainy season (roughly June to October) it becomes a thundering wall of white water; in the dry season it spreads more thinly but the limestone formations are clearer. Either way it is a genuinely impressive sight, and the surrounding Guichun River karst landscape — karst peaks, the clear river, water buffalo in the rice paddies below — makes the journey worthwhile even if waterfalls aren't normally your thing.
The journey here is the main commitment: Detian is in Daxin County in far southwestern Guangxi, about four hours from Nanning by bus. There are direct buses from Nanning during peak season, or you can take a bus to Chongzuo and connect from there. The road through the border karst is striking. A small cluster of guesthouses and restaurants has grown up near the waterfall, and spending a night is a reasonable option if you want to arrive before the tour groups. The scenic area charges an entry fee of around ¥80.