Hawaii draws millions to its shores annually, most of them coming to the islands for idyllic beaches. In such a touristy climate, it may seem like a stretch to claim that you can still find plenty of locales that will afford an entirely unique experience, but it's true.
Completely off the tourist radar and the target of an expensive and ongoing restoration project, Kaho'olawe is an arid but breathtakingly beautiful island that was used for target practice by US bombers for some time. In 1990, military operations were discontinued and Kaho'olawe was placed back under the jurisdiction of the state, which immediately began the restoration.
A second option for a more off-the-beaten-path adventure in Hawaii is Halawa Valley on Molokai. Hike from west to east through a verdant cleft and explore the longest, whitest, and (typically) most secluded beaches in Hawaii.