Waipi'o is an amazingly beautiful, lush valley, all the way at the end of the Hamakua Highway, well off the beaten path. The view from the lookout at the top is tremendous, and many people just come here for the view alone. I come back to see it every single time I've been on the island (three so far).
We've hiked down into it twice, and it was the steepest hike I've ever done - a 25% grade and very hard on the knees - but well worth it. At the bottom it's thick with tropical vegetation, and the Waipi'o River flows out to the sea past a black sand beach. It's about a mile wide at the coast, and if you walk across the shore you can hike all or just part way up a switch-back trail on the far side for different views of the valley. The sides are close to 2,000 ft. high. We ran into a local man on the far side trail who was backpacking over into the next valley with his son to hunt wild pigs.
Thousands of Hawaiians used to live here before the most devastating tsunami in Hawaiian history flooded it out in 1946. It's quite a remote area now, with only a few dozen people here now who treasure their isolation.
You can't drive down into the valley unless you have a 4-wheel drive vehicle; several tour companies will drive you down there if you don't want to do your own thing. There are also options for horseback riding in and around the rim, which sounds more appealing to me. It's on the Hamakua Coast, on the Northeast side of the island off route 240.
My mom lives in Hilo and right down the road from a beach made entirely of lava rock. While this isn't a place to go swimming, it is an awesome place to take in the Hawaii experience. While the waves pound against the shore you get a chance to see them splash above your head. Early in the morning you can see whales off the coast, and all through the day you can see a variety of marine life such as sea turtles, fish, crabs, and dolphins. If you get a chance to visit a beach like this take advantage of it!
The Waipio Valley is at the end of State Hwy. 240. You'll find this beautiful valley and several others along the Hamakua Coast of Northeastern Hawai'i (the Big Island).
There's a 4WD road that goes down into this valley and beautiful waterfalls further inland.
There are tour vehicles that will take you into this valley also - no hiking necessary.