Oahu's leeward flank faces west, out of the winds. Traced north by Route 93 as far as Yokohama Bay, the area is accessible though less oriented towards tourism than other parts of the island. If you're hoping to see some off-the-beaten path beaches, take the road along the coast, stopping to get some water thrills at the Hawaiian Waters Adventure Park near Kapolei in the southwest corner of the leeward stretch before continuing north.
While there are several beaches along this shore that lend themselves to water pursuits like swimming, snorkeling and surfing without resorts as a backdrop there are also other beaches with big swell that do not. Experienced surfers compete on the high break at Makaha, just over half-way up the coast, while board-less visitors wisely stick to the beach. There are numerous places to stop for solitude, though always be careful where you decide to swim, as even when the surf seems mellow the currents can be extremely dangerous.
There are a number of trails that run through the interior mountains that can be reached from the Leeward Coast, although experienced Oahu hikers will be quick to advise caution in these areas that are frequented by hunters and often poorly marked. For those dead-set on exploring the undeveloped side of Oahu there are guided tours available, while the independent are advised to stick to better-known trails.
Yokohama Bay is about 45 miles from Honolulu along Route 93.