Muliwai and Waimanu Valley Trail is a 15.7 mile lightly trafficked out and back trail located near Honokaa, HI that features a waterfall and is only recommended for very experienced adventurers. The trail is primarily used for hiking, walking, nature trips, and birding and is accessible year-round.
Directions from Makapala: Highway 240 leads off Highway 19 at Honokaa to the eastern edge of Waipio Valley. A steep, four wheel drive road extends from the lookout down into the valley. Upon reaching the valley floor, take the road to the right, then follow the beach to Wailoa Stream. The road ends at the stream. Ford the stream and follow the horse trail on the dunes to the west side of Waipio Valley and the beginning of the trail.
Great hike. Challenging but worth it.
Make sure to bring a water filter so you can fill up at each waterfall along the way.
Also, the first big uphill trek is really tough, so it is best to have filled up your water container at the bottom (I learned this the hard way and was pretty parched by the time I got to the top and over to the first stream crossing).
There are lots of mosquitos at the stream crossings so apply mosquito repellent generously at the start of the hike.
Incredible!!!!! Challenging, memorable ... Insanely beautiful
Ok, so here is the down and dirty of the Muliwai trail, and the hike into Waimanu. I had hiked the Kalalau on Kauai multiple times (going as far as you can without a permit), and in many ways this is very similar. To set the record straight, parking at the overlook and going all the way to Waimanu and back in a day is completely possible but heed these warnings: You will be hiking near 20 miles in a single day with CONSIDERABLE elevation changes, and you should not even remotely consider doing it unless you are in very good shape and you can start early.
The road into Waipio is awkward going down just because of the angle of descent, walking to the beach is super quick even though you have over half a mile from the bottom of the road to the beach. It is then half a mile across the valley, the beach has soft sand so it can take time and is taxing. Waipio river is no joking matter, the time I went it was relatively low flow initially, but because of the color of rocks, gauging depth is tricky (poles would be useful here).
Once you finally reach the trailhead at the far end of the valley wall (be sure to take pictures of the Z trail), you are already over 2 miles of traveling in, albeit not particularly strenuous. The Z trail is fickle, while it is of decent width, and always is fairly stable since you are essentially stair climbing the entire way, it is also a 1200' elevation gain in less than a mile and about 1/2 of it is in direct sunlight with absolutely no shade.
Once you reach the fallen needles and the dry forest it is pretty easy hiking, comparatively. The trail is always pretty obvious, and you do undulate up and down a lot, but between the tops of the two valleys, somewhere around 5 miles of "easier" hiking. It is nicely shaded a lot, often a nice breeze will roll though and there is a cute waterfall to break, (as well as some helipad areas).
The hike down into waimanu is steep, the trail is wide and footing normally isn't that bad. It does require going down several hundred feet in elevation on the trail to even get the first glimpse of the pristine valley.
Hiking out of Waimanu is when I had my "oh shit" moment, I realized how tired I already was. I had already hiked roughly 10 miles in, and had to do it back. This time, however, I had to hike out of the valley, hike back to waipio, then down and out of that valley. On the return trip, in ways it is easier but in ways it is more difficult since the most taxing parts are hiking up the Z trail, then on the return hiking up out of Waimanu and then hiking up the road out of Waipio.
Now here is my personal warning: if you do this in a day hike, set a HARD turnaround time, no matter how close you are, otherwise you could strand yourself without proper supplies. Also be wary of the weather, it was starting to get cloudy when I left Waimanu and by the time I had to cross the river back in Waipio it had obviously been raining and the river gained considerable force and grown quite a bit wider. It went to not even waist deep and maybe 40' across, to one part was almost chest deep, and 50' across.
After the hike to Waimanu and then back to Waipio, all I was personally concerned about was getting across the river before weather reared its head, going back to the road and then up the road is a pain but is manageable.
This is one of the coolest experiences I have ever done, and now that I live on the island, I am excited to redo it this time camping instead of doing a day hike. I was at the Waipio lookout around 7:30 and I got back to the top around 5, and I took very very little breaks. So unless you are very fit, and a very experienced hiker do not do it in a day, it is 20 miles of roads and trails, and I am certain you have to lose, and climb, a vertical mile along the way.
It was the most beautiful and challenging trail I've ever experienced. The campsite is the best reward