This is by far one of my favorite hikes on the Big Island. I have venture on it twice. The…read moretrailhead is located in Waipio Valley! Take the very steep road (Kukuihaele Road) down to the valley. When you arrive at the bottom of the steep road, you can go left or you can go right. Right takes you to the beach! Take a left and travel down the town dirt road. You are going to take this road for 0.6 of one mile until you hit a stream in the middle of the road! Do NOT cross the stream (crossing the streams is bad)! There is a trail-head immediately to the left of the road, exactly before the stream road crossing. You walk upwards on the dirt. There will be signs that say, "trail closed," "private property," etc. You will know that is the trail you want to take!
Follow this trail as much as possible and try to stick to whatever appears to be a trail! I try to avoid the homes on the left of the trail as much as possible, to respect their privacy! While on the trail, you will traverse down by the river and back up and down by the river and back up, a few times...that is normal! Then, you will eventually come to many signs saying, "Under surveillance" and more warning signs...you are on the right track! There are two tiny fences you can either climb over easily or slightly go around...not too hard. Then you come to a man-made dam in the river! You will want to cross that dam! I walked in front of the dam, because there was less water. Then, once on the other side, I climb the dam and enter the waist high (depending on your height) water. I stay on the far right side of the ridge until I climb up on the rocks and back on a trail.
Now, keep in mind, the trail will go upwards and downwards, along the river and back up on an actual trail. You will also cross the river several times, because quite frankly, there is no other way to do this hike AND the trail continues on the other side. You go through a bamboo forest too! Towards the last 1/5 of the hike, there is a longer well seen trail on the right side, which will eventually lead you to the Hi'ilawe Falls!
My wife I and I did this hike and we only saw three people (a group) along the way, who turned back, because they did not have enough time to complete it. My wife is on the slower side, so it took us 2.5 hours to get there and 2 hours to hike back. On my first hike when I did this alone, I made the trip back in 1 hour (not sure about the bike there by myself, because I spent more time hiking over boulders and did not notice the trail on most of the journey until hiking back).
A good rule of thumb...stay away from the stream as much as possible! Inevitably, you will have to hike on the side of the stream. Stay away from hiking over boulders as much as possible. The less you have to hike over boulders and rely more on the trails, the shorter the hike will be. Trust me, the trails are there, you just have to look for them and use some blasted hiking common sense.
Wear water proof boots at all possible! I brought a backpack which I carried over my head while in the river at the dam area...only a couple of minutes worth of holding it. There are a few very slippery rocks...keep that in mind. If it looks green and mossy...it is going to be slippery!
Best of luck! Happy hiking!