I liked their signage at the various parks we visited while on the island of Hawai'i. There is a hike down into this valley that is currently closed: https://bigislandhikes.com/waipio-valley
However, as of February the road which is part of the trail is closed to outsiders.
The hike described on this page travels from the Waipi'o Overlook to the beach and back. This is the shortest hike from this trailhead, but there are two other hikes that begin here. See The Muliwai Trail hike, which travels up the cliffs on the other side of Waipi'o Valley for amazing views. Or see Waimanu Valley, a backpack or extreme dayhike to this majestic spot.