Halona cove, Oahu. Beautiful beach right next to the halona blowhole on the southeastern shore. Be careful though...in this area is one of the most dangerous ocean currents in the world, Ka Iwi, otherwise known as the Moloka'i Express. Source: Kanu Hawaii
Insider Tip: For safety reasons, book a tour to see the Pu'u 'O'o flow. There are no paved paths, and good physical condition is required to walk over the sometimes-unstable lava. Best viewing happens after sundown, so many tours walk home by flashlight.
Top 10 Things You Must Do on Oahu, Hawaii - Travel Tips