What are some hidden gems in Hawaii?

Hawaii's hidden gems reward travelers who go beyond the obvious. On Oahu, Electric Beach near Ko Olina draws sea turtles and dolphins to warm power plant outflow — free, rarely crowded, excellent snorkeling year-round. Lanikai Beach on the Windward side has turquoise water rivaling the Maldives. On Maui, the Nakalele Blowhole north of Kapalua shoots ocean spray 100 feet into the air. Waianapanapa Black Sand Beach on the Road to Hana is stunning with free entry (reservation required). On Kauai, the Mahaulepu Heritage Trail near Poipu is an unspoiled coastal hike few tourists find. The Big Island's Green Sand Beach (Papakolea) requires a four-mile round-trip hike to reach, but olivine-green sand is found in only four places on Earth.