This is a natural wonder of the world and a MUST SEE in Vietnam. If you can work this stop into your plans, definitely do!
Travel to Halong Bay: From the Hanoi airport to the town of Halong it is about a 3-hour drive through the countryside and rural villages. Halfway through the ride there is a large complex, which acts as a rest stop for many others, making the same journey to Halong. At the rest stop they sell art, clothing, souvenirs and snacks that are all overpriced, but you will most likely purchase some snacks cause they are unique and interesting looking. The restrooms are clean and they take credit card so no need to spend your dong. This place is made for tourist groups.
After the next hour and a half you will arrive in Halong, which is a cute village on the water with a lot of hotels, seafood restaurants, and small junk boats ready to take people out onto the bay. Junk boats are very rocky, so make sure they supply you with lifejackets.
DO- if possible sleep on one of the small cruise boats that anchor in the middle of the bay. Waking up on the bay is a spectacular experience and you are in an ideal location to access the other attractions of the area.
On these small cruise ships they serve you lunch, dinner, and breakfast the next morning. It is a lot of fresh seafood, so if there are allergies let them know in advanced. Additionally, bring your own bottled water and alcohol if you prefer. Drinks are relatively expensive and you have no other options for staying hydrated. At nighttime, there are many activities to participate in such as, karaoke, cooking demonstrations, and fishing off the decks. There are other boats in the same area, so you do not feel isolated or unsafe on the bay at night.
GO- To the caves. Although tourists are not allowed in many of the caves, there are some that are designed for tourists to walk through. These are well lit, open spaces, with signs and roped off areas to guide you through the large area. The stone within the caves resembles the dementors from Harry Potter and it is amazing that these structures were formed naturally. *Note: If you are claustrophobic you may want to skip the caves.
In addition to the caves, there are also various viewpoints at the tops of the islets in the same area. There points offer beautiful, panoramic views of the bay. You will need to climb hundreds of steep stairs to get to the top for these viewpoints. If you are not physically up to it, do not try. The stairs can become crowded and are extremely narrow to begin with.
Altogether, Halong Bay is an incredible, and mystical, and earns its title as a wonder of the world. You may see photographs of the site, but no photograph can truly capture its magic.