Fed by 40 feet of rain annually, the Wailua River is the only navigable river in Hawaii. It snakes through Kauai's east side to the spectacular Wailua Falls. In Wailua, turn off Hwy 56 Kuhio Hwy (Rt 56) at Kuamoo Rd and drive to scenic overlooks.
Farther up is the Fern Grotto which is reachable by boat. The King's Highway is the navigable portion of the river that leads inland and was the scene of religious processions and festivals.