It is one of my favorite trails. Hard to say why. I might try to cite a few: it is an honest trail, it keeps going up, hardly ever goes down; it will almost never make you muddy, it fact it is a mighty boot-cleaner; it is so long and exhausting that it is almost at the limit of a day hike, you will get a wonderful sleep that same evening; the trail is hard, but it never becomes dangerous, so you never have to psyche yourself up in addition to preparing for physical exertion.
From Farrington Hwy, if you turn right on Maiuu Road and go straight until the road makes a left turn, you will bump right into the trailhead. We usually don't park there, probably afraid that our cars' safety, but we park at the intersection of Ala Akau, and then take Kaulawaha, which turns into a trail for a few minutes, to come to the same place.
The trail is honest and straightforward: just walk/climb up. Crawl over an abandoned waterpipe or flume. Few hundred feet up is the Kamaileunu Heiau. Volunteers are restoring and maintaining the heiau. Keep going up along the fairly steep ridge. In one hour or so, the trail flattens.
"Flatten" is relative, it is actually still going up, but at a slower pace. About 40 minutes later, the trail resumes its fairly steep climb, through a lot of cacti. The purple cactus fruit is quite delicious, but there are thorns all around it, and don't eat the thorns!
The steep section probably takes more than an hour. Then the trail actually goes down a steep rock. Even though it looks dangerous, looks are deceptive, and it is actually quite safe, and you don't even meed a cable (and there is no cable!) After you come down the rockface, there are a number of humps on the ridge ahead of you, most of them look quite unclimbable. Generally, the trail goes round to the right to climb these humps, and yes, you have to get through all of them, maybe five altogether?
That takes up another hour. Eventually the trail goes up a bare and fairly steep slope, to arrive at a tree (there may be actually more than one tree there, memory fails me ...) near to a low-lying rock formation. Some people claim this is the highest point of the trail, some say it is the hump 15 minutes ahead. Anyway, the trail truly levels off at this juncture, and the walk is almost easy, provided that you have not yet developed cramps in your legs. You go up and down several very minor humps, and finally arrive at another low-lying rock formation.
It is the unmistakable end of the trail, even though someone put a flag there to mark the spot. Beyond that point, the trail goes down fairly steeply down a saddle. But it is beyond the saddle that fearsome rocks and cliffs reign for a half mile, that prevents any more progress without technical aids. Oftentimes you see mountain goats running up and down the cliffs in a family outing. After this half-mile section, eventually the trail becomes hikable again, and in fact it leads all the way to the top of Ka'ala, becoming the Waianae-Ka'ala trail. To the left, there is a trail going straight down into Makaha Valley. Fred Dodge and company have done it and claims it is doable, but looks rather challenging to me.
The fastest time I ever managed going up was 4:10, and the return trip, by the same route, takes almost as long, I think because one has to be careful going down the fairly steep slopes. The trail goes from literally sea level to 32xx feet. After Ka'ala and Kalena, this is actually the third highest place on Oahu, higher than Kaua or Konahuanui.
BTW the Kamaileunu arching ridge top can be seen clearly from the summit of Lanipo trail.