The northeast quadrant of the Big Island (north of Hilo, south of Waipio Valley) is as lush as any coastline in Hawaii. You can drive some 40 miles, hitting well-known attractions like Hawaii Tropical Botanical Gardens, Akaka Falls State Park, and Laupahoehoe Beach Park—site of the killer tsunami of 1946.
The cool tip for this drive is to take several segments of the Old Mamalahoa Highway, which have been bypassed by the newer two-lane blacktop. The old road penetrates lush tunnels of greenery, goes through historic sugar cane settlements, and then rejoins the highway. Leave your snorkeling gear in the car, since you won't find beaches, but adventure seekers can find several surfer coves.
If you want to spend the day and really get out there (or up there) take one of a few roads that climb several thousand feet to one of Hamakua's forest reserves that lie along the lower slopes of Mauna Kea. For details, see Hawaii the Big Island Trailblazer, pages 169 to 175.