Spend the day lounging on a Kohala Coast beach (Hapuna, Kauna'oa -- also known as Mauna Kea -- or Kua Bay), but throw jackets and boots in the car because you'll be catching the sunset from Mauna Kea's summit. Bundle up and stick around after darkness falls for some of the world's best stargazing. Book a tour or head straight for the visitor center, join their free tour of the summit at sunset, and return to the center to use their telescopes.
Hike Volcanoes
Devote a full day (at least) to Volcanoes National Park. Head out on the Kilauea Iki trail -- a 4-mi loop at the summit -- by late morning. Grab a sandwich at the Volcano House when you've finished and take in their fantastic views of the craters. After lunch, head down Chain of Craters Road to the coast and the active lava flows. Bring water, snacks, and a flashlight if you intend to hike out to the end of the road where the lava flows into the ocean. Start your hike during the day (by 4 PM or earlier) to ensure that you're as close as you can safely be when night falls and to prepare yourself for a spectacular nighttime lava show.
Majestic Waterfalls & Kings' Valleys
Take a day to enjoy the splendors of the Hamakua Coast -- any gorge you see on the road is an indication of a waterfall waiting to be explored. For a sure bet, head to beautiful Waipi'o Valley. Book a horseback, hiking, or 4WD tour or walk on in yourself (just keep in mind that it's an arduous hike back up -- 25% grade for a little over a mile). Once in the valley, take your first right to get to the black sand beach. Take a moment to sit here -- the ancient Hawaiians believed this was where souls crossed over to the afterlife. Whether you believe it or not, there's something unmistakably special about this place. Waterfalls abound in the valley, depending on the amount of recent rainfall. Your best bet is to follow the river from the beach to the back of the valley, where a waterfall and its lovely pool await.
Underwater Day
Explore the colorful reefs populated with tropical fish off the Big Island's coast for one day, and we defy you to stop thinking about the world beneath the waves when you're back on land. Our favorite spots include Two Step (near the Place of Refuge), Kealakekua Bay, and the Kapoho Tide Pools. Early morning is the best time to see the Hawaiian spinner dolphins that frolic off this coast, but you're likely to see turtles any time of day, along with yellow and white angel fish, spotted Moray eels, trumpet fish, and a myriad of other brightly colored varieties.
Volcano Hotsprings & Boiling Pots
Most tourists skip Puna. Venture into this remote area for a morning, and you'll be rewarded with lava tube hikes (Kilauea Caverns of Fire), volcanically heated pools (Ahalanui Beach Park), and tide pools brimming with colorful coral, fish, and the occasional turtle (Kapoho). Head to Hilo in the afternoon to catch a glimpse of the Boiling Pots waterfalls, Banyan Drive, and Queen Lili'uokalani Gardens, before dining at one of Hilo's great restaurants.
Pololu & Paniolo Country
North Kohala is a world away from the resorts of the coast. Visit the quaint artists' community of Hawi, then head to Pololu Valley for amazing views. A steep-ish 1/2-mi hike leads to a fantastic black sand beach surrounded by beautiful sheer green cliffs. Back on the road, head up Highway 250 to Waimea and the pastures of paniolo country. Indulge in a memorable meal at one of the fantastic restaurants (we recommend Merriman's, Daniel Thiebaut, or Edelweiss).
Go Off-Road
Book an ATV tour or take your 4WD for a spin to check out some of the Big Island's isolated beaches. There are green beaches (in addition to "the" Green Sand Beach) waiting in the Ka'u region and ruggedly beautiful white beaches with perfect turquoise water along the Kohala Coast; deal with the tough, 4WD-only roads into these beaches and you're likely to be rewarded with a pristine tropical beach all to yourself.