The Fern Grotto is located in a unique, albeit small, state park along the Wailua River. The grotto can only be accessed by boat, kayak (normally) or stand-up paddleboard. The location is named for a large mouth cave that has been reduced in size over the last few decades by floods and a ceiling collapse. It once hosted weddings and live music, but it is now only visible from an observation deck. The setting is very pretty with the many ferns and vines growing around the entrance, though there is apparently much less vegetation now than before Hurricane Iniki in 1992. There is a smaller waterfall near the grotto and a botanical garden lining the pathways between the dock and the grotto. You can take boat tours here or use SUP's currently, and eventually visitors will be able to kayak in again after repairs are made from the April 2018 floods. Don't use the boat dock if you are on a watercraft because that is where the large barges dock; instead, there is a earthen ramp to the right of the wooden dock for smaller vessels.