This Saturday was the 2nd time I did Pu'u O Kona, but it's the first time I've done it from Mauna O Ahi Ridge. The other time was from the Kuli'ou'ou Ridge trail. The Mauna O Ahi trail is very well trodden and easy to follow. Being that it's somewhat of a secluded trail and one that is less traveled, I'm going to keep the trailhead a secret. The only hint I'll give is that it starts at the same trailhead for both the Kuli'ou'ou Ridge and Valley trails.
Mauna O Ahi consists of dropping into a valley, crossing a small stream, and climbing steeply to the Ko'olau Summit. At the summit, we turned left, eventually reaching the terminus of the Kuli'ou'ou Ridge trail. The sections along the summit offer awesome views and dangerous drop-offs. This day was hands down the most windiest day I've ever hiked, and I recommend not doing this hike with high winds. Coming down the west ridge of Kuli'ou'ou was insane! The wind felt like a hurricane in the mountains, and walking across the narrow sections felt like we were going to get blown off. Check out the video.
Words cannot express how fun this hike is. It's a short, dangerous, and beautiful loop hike. You don't have to park two cars in different places to do it either. In my opinion, it's one of the funnest loop hikes on the island. A longer write-up of the hike can be found here: http://kaleolancaster.blogspot.com/2008/06/puu-o-kona-via-kuliouou-ridge-june-11.html
The west ridge of Kuli'ou'ou Valley has some narrow spots as well. It was very windy here and a bit scary.