Cat Ba
Cat Ba island is in Ha Long Bay. In late April on a particular 3-day weekend, Vietnamese go to Cat Ba by the thousands. What is a sleepy island during the winter, suddenly becomes full with people arriving on high-speed ferry boats and romantic junks with red sails.
My friend invited me on a trip along with several other people. He arranged a private car, high-speed ferry tickets, and a hotel. From Hanoi, we drove to Hai Phong, a centuries old port on the Red River delta.
Map locating Hai Phong municipality in Vietnam. Made for Wikipedia by uploader.
At the port, we boarded the ferry and one hour later we pulled into Cat Ba bay, passing between hundreds of small fishing boats as we approached the dock. We walked to our hotel and began a lovely four day, three night vacation on an island with nothing more to do the eat seafood, drink coconut juice, and relax on the beach.
The Vietnamese tend to do everything together. Early in the morning the beach is desolate. Then, it gets very busy until about 11:30 AM. It is deserted during the time everybody eats lunch back in their hotels. Vietnamese are not at all fond of having a suntan, so they come back to the beach late in the afternoon, almost as the sun is setting, and swim until dark. All of them come at once. Thousands decend down stairs to a small beach to swim, bury eachother in the sand, splash, chase, and otherwise enjoy the beach with bounding energy. The general population is quite modest in dress. Vietnamese ladies wear skirt-bottom suits. Vietnamese men wear underwear under swimsuits. You ask how do I know? Well it's quite obvious, often, the underwear is larger than the bathing suit!
We took some time one day to kayak, and another to ride motorbikes around the island. It contains a national park with rare monkey and cat-like animals. 
For dinner one can take a small boat 
to any one of many floating restaurants for fresh from the bay seafood. We had a feast of seafood every day and night. 
