While in northern Vietnam, we did a homestay in Ba Be National Park and took a 5-hour boat ride that included a stop at a limestone cave filled with bats, lunch with a local family, and a hike to a waterfall.
My friend and I rented a motorbike and then putzed on over to Ba Be National Park. What we found was a lively collection of locals on a staycation, and thousands of tiny fish enjoying the splendid view of the lake. We succumbed, along with the locals, to taking a boat trip around the lake, and drinking in splendid sights such as, "the Bat Cave," and "the Fairy Pond," and "the Pagoda Island." It was, actually, worth the trip, and the $15 for the boat ride. (Even if the Fairy Pond was underwhelming.)