For a peaceful yet substantial ramble, take this 9-mile loop traversing meadows, lava flows and pretty kipuka (oases) forests filled with koa and ohia trees. It's one of the best places to see native birds including the illusive ʻiʻiwi: the iconic scarlet-colored honeycreeper which is increasingly scarce at lower elevations. The signed trail goes south from Saddle Road at Mile 22.5.
This historic trail was used by ranchers driving cattle from the highlands to waiting ships in Hilo, and runs along the edge of the 38,000-acre Kipuka Ainahou Nene Sanctuary, established in 1974. Historically, the trail continued across the road, circumnavigating Mauna Kea to Waimea, but access issues and lack of maintenance are wiping it off the map.
The trail is marked by ahu (stone cairns); it's easy to follow in good weather, less so in rain or fog. If in doubt, retrace your steps to find your way back. Eventually the trail connects with Powerline Rd (marked with a sign), a 4WD road that can be used as a return route, although this road dumps you about 1 mile from the trailhead parking area. Don't leave valuables in your car.