For sure the half-mile loop hike at Akaka Falls State park is a tourist trot, complete with sightseeing buses and paid parking. But it's also one of the best waterfall-and-botanical hikes in Hawaii.
The park is a four-mile drive up from the quaint town of Honomu on the south end of the Hamakua Coast (the northeast quadrant of the island.) Besides Akaka's 440-foot freefall of whitewater, the hike also takes in Kahuna Falls, which spews from a side-canyon, and a profusion of tropical greenery alongside Kolekole Stream.
Stairways, bridges, and paved sections make for easy going. If you show up in the morning, say before 10, you'll have the place mostly to yourself.
Hamakua is the lush coast of the Big Island, with many streams and valleys, with jungly sections of the Old Mamalahoa Highway that offer opportunities for side trips—rugged coves, beach parks, and old sugar-shack towns. You can also take roads up the mountain (the 'lower' slopes of Mauna Kea) to vast forest reserves. This isn't the coast for a day at the beach—surfing, yes, but swimming, no) but Hamakua is dripping with eye candy.
Hawaii the Big Island Trailblazer has the details on Hamakua's hidden attractions, on pages 169 to 176.