Na Laau Trail is a 2.5 mile lightly trafficked out and back trail located near Honolulu, HI that features a river and is rated as moderate. The trail is primarily used for hiking and is accessible year-round.
This is a little known trail that contours the north and west outer flanks for Diamond Head Crater. This trail is named after the once public Na Laau Arboretum that used to be on the south outer flank of Diamond Head just below the highest point of Leahi. It is now closed and owned by the DNLR who is supposed to improve it and reopen it to the public. This will be an incredibly slow process as the state does not have the funds to do so at this time. So hike at your own risk. Most of the hike is on a moderate trail that is currently overgrown. Watch out for slippery sections in sandy areas. There are good views of the ocean, Honolulu and the Koolaus.
There are some 21 different ridges (as documented by Wing Ng - http://www2.hawaii.edu/~turner/hikes2/dhead.htm) all around Diamond Head that can be taken from the bottom up to the crater rim.
This is a little known trail that contours around the north and west part of the base and was originally part of the Cannon Club to Na Laau Arboratum. The route we took was from KCC, to the Cannon Club, past the state fenced area, and to the old bunker building with the rail tie. We will leave visiting the old arboretum for another time. The Na Laau Arboratum, for which this trail is named, was originally established by George Campbell Munro, an ornithologist who was born in New Zealand and immigrated to Hawaii in 1890. Read more about Munro here: http://the.honoluluadvertiser.com/article/2007/Jul/08/il/FP707080302.html
Note that this is now all owned by DNLR and they do not encourage hiking here. Enter at your own risk. The way is very overgrown so long pants is encouraged. Footing can also be loose on the open sandy areas. There are some ribbons along the way, but its hard to get lost here... Finally, you will find a few homeless tents and extravagant luxury homes, be mindful as you would walking past any housing in close proximity.