This company has a few boats that will take you to Bai Tu Long, the less visited part of Halong Bay. We did a two-day / one-night cruise, which is really 24h from noon to noon. The food was excellent and the rooms very comfy and clean. We stopped at a cave, did 1h of kayaking, swam, visited a floating village, and one of the crew members (who calls himself Harry Potter) showed some magic tricks after dinner. We would recommend the 3-day/2-nights tour to make the most of the time in this beautiful region.