I'm not one for crowds or noise, so when I happened upon a tour for Bai Tu Long Bay, north of its more popular and populous Ha Long Bay, I jumped on the opportunity.
This bay is also a national park, but the number of tour companies and boats allowed in are restricted by law, so there are far fewer boats. Granted I didn't visit Ha Long Bay, the other guests on my boat said this was just as scenic but less people. Perfect.
We were still able to go kayaking, but there weren't any caves in the area we stopped. On the plus side though, we were able to do a home-stay and go to the beach on a tiny island 2 hours from shore.
There are tours that offer both bays, and given the long commute from Hanoi, it wouldn't be a bad idea to cover both if you're there anyway.