Attempting to get to Cat Ba Island without a packaged tour was near on impossible. Cat Ba island is close to the Vietnam mainland, next to the world renowned Halong Bay. We originally wanted to get a bus to Halong Bay where we would find our own way to the island, but the tour guide on our bus convinced us that it would be too hard and that we should go with his group for a day tour of the bay which would drop us on the island at the end of the day. It turned out the day tour was very average, the "kayaking trip" involved him giving us kayaks and telling us to be back in 20 minutes, which wasn't even enough time to get to one of the karsts. We met people along the way who had tried to do it alone and they had endured scams on top of scams. They were supposed to arrive at midday but got to Cat Ba town with us at about 5PM after spending the whole day waiting for other tour groups to do things and not being able to find any food.
Luckily for us, this group of 8 people turned out to be great to hang around with, so we stuck with them for our stay on Cat Ba Island, spending a full day kayaking on Lan Ha bay, which is the equally beautiful but lesser known alternative to Halong Bay. Kayaking on Lan Ha bay was, in one word, excellent. We were taken through caves into pristine lagoons that were only accessible a few days in the year due to the weather and tides, even the guides had never been there and were even more excited than we were. We shared the lagoons with only a couple of the local fishermen, the swarms of tour boats on Halong Bay couldn't access the areas due to the low overhead clearance. We felt very lucky to have been able to visit the area and stopped to appreciate the silence that was only broken by the wildlife.
Lan Ha bay is very well worth the effort it takes to get there and has been one of the highlights of our trip so far.