Easily the best thing we did on our Ha Long adventure. I will never, ever forget kayaking out into the sea in the pitch black of night then swimming with glowing plankton under a beautiful starry night. Worth every penny. One tip - don't expect to see them glowing underwater from the boat, like the northern lights in water. They only glow when you put your hand (or body!) in the water. But swimming with them was so special. The guide, Linh, was hilarious and he arranged a birthday cake for my wife too which was so sweet! Towels are provided, as is dinner with plenty for vegetarians and vegans. Take some bug spray in case of mosquitos, some swimming gear and some cash for drinks