We spent two days and one night on the water off Cat Ba Island. This is south and west of Ha Long Bay, which has apparently become super busy (625k visitors in one three day weekend).
There is plenty of tourism here, which we were clearly part of, but there is also a fascinating community of fishers and farmers who live on the water. They are served by supermarket boats that trade other goods for their catch. Their floating houses have extensive solar, TV, wifi, even AC.
The geology is remarkable. These mountains rise up in various globular shapes, and are riddled with undercut caves and pass throughs formed by wave action. The entire area is sheltered from the open ocean by the extensive island system. It seems pretty idyllic.
Our boat was great. We were on a 5 cabin boat, so 10 customers (the four of us, a young recently engaged couple from Germany, a veteranarian and ob/gyn doctor couple from Morocco, and a pilot / nurse Kiwi / Aussie couple), our host "Handsome John" (I became "intelligent John"), the bartender, a captain, and one other helper / cook.
Somehow the kids lucked out, scoring the biggest cabin in the stern of the boat. Laura and I were in more intimate accommodations amidships. Meals were served under a sun canopy on a beautiful table, and often included interesting choices.
We enjoyed kayaking, swimming in the almost-too-warm-to-be-refreshing water, and jumping off the boat.
And, oh, the sunset.