Hikinaakala Heiau

"Take a riverboat up the Wailua—which translates asthe "river of the great sacred spirit"—fed by the Mount Waialeale shield volcano, one of the wettest spots on the planet. Seven temples once stood along Hawaii's longest and only navigable freshwater passage.Today, the remains of four are still visible, alongside petroglyphs and rocks where the island's alii (royalty) would give birth. Stretch your legs at the stunning Fern Grotto: Verdant plants blanket the roof of the volcanic-rock cave there. Smith’s offers 80-minute tours there on open-air boats, which include the songs and stories of ancient Hawai'I, plus a bonus hula lesson (smithskauai.com)."