The Ko'olau Summit Trail roughly follows the spine of the Ko'olau Volcano's western flank from Pupukea to the junction of Kipapa Trail high above Waiahole Valley. There are several associated trails which feed the KST from both the leeward and windward sides of the island along the way. From my reading there was no master plan to build this network, it came about as a result of the combined works of the US Army and Charles S Judd who served as the Territory of Hawaii's Forester. The army's motivation was training and troop deployment and the Forestry Division's motivation was pig eradication and tree planting. The interaction between these two forces resulted in the cooperative construction of trails which were eventually linked together into what is known now as the Ko'olau Summit Trail during the 1920's and 1930's with depression era stimulus spending. With the end of the depression and the outbreak of World War II the Civilian Conservation Corps was shut down and the newly constructed trails were soon left to languish. Despite being over 80 years old, most of the trails remain somewhat passable but can become very obscure at times. Some are no longer open for the public as they are not on public lands, others can be accessed via permit from the State, US Army, and landowners, and some are open to this day. Many are passable but some have been reclaimed by the vegetation.
For more history of the construction of his amazing network of trails Stuart Ball's latest book "Native Paths to Volunteer Trails- Hiking and Trail Building on O'ahu" is the hands down best source.
At the time of it's construction the the entire summit from Kipapa to Pupukea could be done in one day. Now that feat would be impossible. The trail is notoriously muddy, often overgrown, and sometimes seems to vanish. The Ko'olau Summit is often cloudy making what is already a difficult to follow trail nearly impossible. Hiking at night on the KST would be extremely hazardous. The uneven ground and exposure in some sections to drop offs of more than a thousand feet mean this trail should only been done during daylight hours. There is little traffic on the trail and at least one person in the recent past has simply vanished without a trace.
In my opinion, tackling the KST without any experience would be ill advised. One should familiarize themselves with the various trails leading to and from the summit before attempting to do the summit trail itself.
The links below are for reference only and are based on my memory and experience only and absolutely should not be relied upon for navigation or any other purpose.
Ko'olau Summit Trail Segments
Pupukea to La'ie
Pupukea to Kahuku
Pupukea to La'ie via Kawailoa Trail
Malaekahana to La'ie
La'ie to Castle
Pauao to Castle
Waikane to Pauao
Waikane to Kipapa
Papali Uka to Castle Trail
I will add more to this page as time permits...