Ha Long Bay
Ha Long Bay (also "Halong Bay")  is in northern Vietnam, 170 km (105 mi) east of Hanoi. The bay is famous for its scenic ocean karst topography and is often included in lists of natural wonders of the world.
"Ha Long" means "Bay of Descending Dragons" (Chinese: 下龙湾; Xiàlóngwān), though prior to the 19th century this name was not recorded in any document or archive. When mentioning the present-day Quang Ninh Sea or Ha Long Bay, old historical books often referred to them by the names of An Bang, Luc Thuy or Van Don. Not until the late 19th century did the name of Ha Long Bay appear on a French Marine Map. The Hai Phong News, a French newspaper of the time, had an article, Dragon appears on Ha Long Bay, reporting the following story: In 1898 a sub-lieutenant named Lagredin, captaining the Avalanse reported seeing a huge sea snake on Ha Long Bay. This was also witnessed by many of the crews. Thus emerged the European image of the Asian dragon. Whether this appearance of a strange animal looking like a dragon resulted the name of Ha Long Bay is not known.
The Ha Long Bay archipelago is made up of 1969 islands, both settled and uninhabited. These can be accessed from various ports, though in the special case of Cat Ba you can also arrive either by car, motorbike or bus (via Haiphong) or combined bus/boat (from Hanoi via Halong City).
From Nanning in China's Guangxi province, the Nanning International Tourist Distribution Center (有爱南路10号(中华路口); Yǒuàinánlù shí hào (zhōnghuá lùkǒu); #10 You'ai Nanlu on the corner of Zhonghua Lu) provides daily buses to Halong City (170元, 8 hours) at 7:30AM.
There are many package tours from Hanoi, Standards on these vary. Some of them are very good indeed, offering comfortable - or even downright luxurious - boats, excellent food and knowledgeable and enthusiastic guides. Others - particularly at the cheapest end of the market - may be characterized by long and crowded bus rides, tourist-oriented rip-off trips on boats so slow you could swim faster (to get you to buy more food and drink on board), and other shady practices. Ask around other travelers before parting with any money.
The islands can be accessed from various ports.
Helicopter trips can be taken from Gia Lam Airport in Hanoi.