Rent a car, exit airport, turn left, and then make the first left towards the state park. The road is bad.. well, actually not bad at all by big island standards. At the end is a wonderful beach. If that is too scary for you, turn right out of the airport (or heck, just hitchhike; it is the big island after all), and make the first right towards the 'natural engergy lab'. Go down and hang out around the tide pools, enjoy the sunset island style.

The former is about 20 minutes of driving (mostly going real slow over the road to the beach), is closed on wednesday, and they close the gate at sunset if I remember correctly. The latter 5 minutes from the airport. No traffic worries. FWIW these are the places you'll see as you land/takeoff from Kona (in either direction)