Maui's Hana Highway hugs a jungled coastline, crossing mossy one-lane bridges, botanical gardens, and umpteen spewing waterfalls. The Big Island's Old Mamalaoha Highway on the Hamakua (northeast) coast does pretty much the same thing—only without the traffic jam of rental cars.
The trick is to take side-trips from the higher-speed Highway 19 (on the run from Honoka'a south to Hilo) onto the hardly-used sections of the old highway. In places, vines hang down nearly to your windshield and leafy sprays are at arm's length out the side windows.
A few miles off the highway is Akaka Falls State Park, offering a chance to take a .5-mile loop trail through a tropical garden, passing two waterfalls.
Akaka Falls is a classic, dropping about 500-feet through a split in a cliff.
Though the raising sugar cane days are over in Hamakua are over, about a half-dozen sleepy towns remain, like Honomu (above). In several other towns you will find intact enclaves of sugar-shack communities.
Umauma could be the cover shot for Waterfalls Magazine (if there was one). The triple-decked cascade is near three botanical gardens, including one of the best in the state—Hawaii Tropical Botanical gardens.
Hawaii Big Island Trailblazer has more details on Hamakua—there are numerous beach parks as well. Most people zip along this coast on the way to someplace else, without realizing a fabulous destination is at hand.