The journey as much as the destination has kept this tourist attraction popular since 1946, when the Smith family first began offering boat trips 2 miles up the Wailua River to this lava-rock cave with lush ferns hanging from its roof. The open-air barge cruises past royal and sacred sites of antiquity, noted by a guide, until it arrives at a landing that’s a short walk from the grotto. Ancient Hawaiians knew it as Maamaakualono, a site dedicated to the god Lono, who is associated with agriculture and healing. Although you can no longer enter the cave, an observation deck provides a decent view, as well as the stage for a musician and hula dancer to perform the “Hawaiian Wedding Song” (made famous by Elvis Presley’s 1961 film Blue Hawaii, filmed nearby at the Coco Palms). The tour, a total of 80 minutes, includes music and hula on the return trip down the state’s longest navigable river (see “Wailua River State Park”). Note: Kayakers and other paddlers may visit Fern Grotto on their own, as long as their arrival or departure doesn’t overlap with those of the tour boats; see “Kayaking” for rental information. Kamokila Hawaiian Village, across the river from the grotto, also offers guided outrigger canoe tours and rentals.