Between 8 and 9 in the morning, you'll see dozens of minibusses plying the streets of Hanoi. They are picking up their passengers for a tour to the famous Ha Long Bay. You'll see the same minibusses over and over again when driving the 3.5 - 4 hours to Ha Long, and the same tourists will be on your boat or the one next to it. Ha Long Bay is an extremely popular destination both for foreigners and Vietnamese: already in the early 1990s, it saw over 1 million visitors a year. It is unlikely that that number has decreased over the years - so there will always be about 3,000 other people in the Bay at the same time as you!
I visited just a week after the fatal accident that killed 12 people here on an overnight boat. Traffic seemed to have resumed as normal. Overnight stays are also possible again, some of my group went on to stay for 1 or 2 nights on the boat. I opted for a day trip only: not because of the accident, but also since I usually get bored pretty quickly looking at "natural beauty". And I had heard bad reports about life on board the ships: I knew that I had made the right decision when I overheard the guide speak to the others about the evening program that would constitute "drinking and karaoke".
The natural beauty of the Bay lay hidden today under a very common fog. As I had already seen the similar karst landscape at Yangshuo/Guilin in China a couple of years before, I cannot really say that I was blown away by it. We went onto one of the islands to visit the Surprising Cave - a indeed surprisingly big and beautiful cave with three hollow chambers. We saw some monkeys here too, just outside the cave exit.
Part of the tour also was half an hour of kayaking - enough to paddle a full circle around the main area. The views from the kayak I found much more impressive than from the larger boat: you're so tiny then and the peaks rise sharply in front of you. I had a better look at the water too, and cannot say that I saw pollution by plastic or other junk floating around (contra dictionary to most of the reviewers below). There is a thin layer of oil on the water in some parts though.
And then it's time to get back on the bus to Hanoi, another 3.5 hours. It has been somewhat of an obligatory trip, to tick off the WHS. However, the tour was carried out well (good seafood for lunch) and I had a satisfying day.