Halong Bay is located in northern Vietnam, about 170 km away from the capital Hanoi. There are about 1,600 islands creating a magnificent view.
If you have enough time in Halong, I recommend you to take one of Halon Bay cruise tours.
But if you do not have enough time, then Halong Bay helicopter tour is an option. Helicopter departs from Tuan Chau Heliport (see google map) near Halong Bay.
However, after a helicopter crash, helicopter tours are halted.