On my first trip to the islands in 2003, I took along my logbook, airman's certificate, and medical certificate and rented a C-172 at Hawaii Flight Academy. Having never rented there before, I had to fly with their instructor (which was fine with me since flying in Hawaii is so different from any other environment I've ever flown in before). IIRC, it took us about two hours for a leisurely circumnavigation of the entire island with plenty of time for circling over Pu'u'O'o and Kilauea. While flying offshore, we generally stayed around 500' above the water, which gave lots of opportunities for spotting whales and huge manta rays. I highly recommend the experience for pilots and non-pilots alike.