Ka'a'awa, Hawaii

The mountain range that runs along Oahu's eastern edge is all that remains of a single, enormous shield volcano. Now known as the Ko'olau Range, this 34-mile stretch of steepled ridges was part of the massive rim encircling Ko'olau Volcano's crater, until an eruption sent most of it plummeting into the Pacific Ocean over 10,000 years ago. Small beach communities now dot the narrow windward shore between the peaks and the Pacific, giving it a rural feel in contrast to bustling Honolulu.