Just behind the Dillingham Airfield is a zig-zagging trail going up the hillside.
It's the Kealia trail, and it'll eat your sneakers.
Exit the highway just west of the airfield and park on the UNICOM parking lot behind the airfield. Ignore the signs saying "Keep Out". Be mindful of the one informing you that this is a military training area - it's the one with bullet holes.
Then start your ascent.
You'll proceed along a series of switchbacks, giving you a magnificent view of the north-western shore of Oahu. The ascent is relatively easy, but make no mistake: it's exercise, so bring water - you'll need it.
After the switchbacks you'll come to a little picnic table where you can catch your breath before going farther up.
I turned around at a perforated sign informing me that I was entering a public hunting area. (It seemed safest so.)