Beyond the Gate D entrance above Dillingham Airfield, the 2.5-mile, one-way Kealia Trail switchbacks steeply up (there's a 1660ft elevation change) through exposed country with ocean views along the way. It connects to the 2.5-mile, one-way Kuaokala Trail, which brings hikers to a justly celebrated ridgetop viewpoint over the Makua Valley and Waiʻanae Range.
Note that access to the Kuaokala Trail is physically easier from the Waiʻanae Coast but requires an advance permit to approach via the Kaʻena Point satellite-tracking station. Both trails are open to mountain bikes. Print out a topo map if you go; allow six hours for both. There's detailed trail information on the website.