Extending north from Hilo for about 50 miles, the Hamakua Coast is one of the best tropical greenery drives in Hawaii, especially if you take the numerous opportunities to veer off the new highway and twist through segments of the old blacktop.
The Old Mamalahoa Highway is often through a tangled tunnel of drippig flora, passing gushing streams and several waterfalls, such as Umauma Falls (pictured), on a short side trip to a botanical garden. The highway also features sugar-shack towns—more than you can find anywhere else in Hawaii—like Honomu (pictured) at the southern end of the route, just off the main highway on the way to Akaka Falls State Park.
Set at 1,000 feet or more above sea level, Hamakua is not a beach-lovers drive. The only place to get down, at Lapahoehoe Beach Park, is a wave-battered seascape known infamously as the place where the "sea went beserk" in 1946 and a tsunami took the lives of 32 people, including 21 school children.
You can easily spend a long day exploring Hamakua's offerings, but few visitors do, since the Big Island is, well, big, and vacations are short. You could spend another whole vacation just heading mauka the highway, up to the lower slopes of Mauna Kea, to several state forest reserves. A four-wheel drive helps on some of these excursions. Pages 169 through 176 of Hawaii the Big Island Trailblazer covers the place in detail.