We decided to skip the crowded Halong Bay and go for a boat trip to the much less frequently visited (by foreigners) Bai Tu Long Bay. In summer this bay is very popular with the local tourists and many islands can just be visited by them. We decided on a tour with ethnic travels because we were afraid to end up on a party boat.
The choice was perfect for us. We got to travel on a nice wooden boat with just our little group amd see the very quiet bay with its karst mountains sticking out of the sea water. We went to a very pretty Island with white beaches, took a quick swim and rode into the sunset on bicycles, not to forget kayaking through am oyster farm the next day. After returning to the Harbour the next day, we took a nutshell or small rowboat, as you wish, to a mini island with a cave/ aquarium building site and a beautiful view over the misty bay. 
Then we visited a family in one of the floating villages. A vibrant trip with fun guides, awesome drivers and good food. We can make vietnamese spring rolls now! They are my favourite ❤