East of Waimea and northwest of Honokaa on the Big Island, there is an adventerous route to the base of the 1,450 foot HiIlawe Falls in the Waipi o Valley.
To reach the trailhead from Honokaa, head west on the state route to the overlook over the Waipio Valley. Continue down the steep road into the valley. Stay to the left at the first intersection near the bottom. Shortly, the falls will come into view ahead. After crossing the creek, park along the road.
The trail starts just over the creek on the left side of the road near a speed limit sign. There maybe some PVC pipes marking a route to a rock wall. Turn left at the wall and follow the vague trail to the stream. Cross the stream to the left bank and head upstream for 100 yards. Pickup a more distinct trail and continue upstream to the dam. Enter the water and skirt the left shore line through the deep water. Exit the water on the faint trail which runs 50 feet to a rock staircase. Climb up 20 feet and rock hop to the bamboo forest to reacquire the trail. It reaches the stream again. Cross to the right side and follow upstream to the falls.
As is common on the Big Island, the property ownership along the route is questionable.
Here are some notes on adventuring in Hawaii. First, unlike mainland forests, the tropical island forests can grow very dense and can mask dropoffs. Plus, the trails can be very wet and slick most of the year (December to February is the main rainy season, but expect rain all year round). Stay on the trail to avoid disorientation. Second, speaking of disorientation, be aware that most Hawaiian topographic maps use the Old Hawaiian Datum. When trying to use the latitude/longitude from those maps with a GPS unit, you will think you are 0.4 miles south/southeast of where you really are. Kind of important in a dense jungle. Third, the bacteria Leptospirosis is found in the local waters and mud. It causes flu like symptoms within 2-20 days of contact, and can be fatal if not treated with antibiotics. Fourth, when hiking about, walking sticks can be very helpful for stablity in the slick conditions, for probing mud hole depths and clearing webs of the tiny crab spider.
Overall, HiIlawe Falls is the 2nd most popular hiking trail of all 45 hikes in Hawaii.