The closest beach is at the Marina/Harbor (Honokohau Harbor). We are about 10-15 minutes away. The marina/harbor is on the same highway as you exited from the Kona Airport. There are several beaches to go to at the marina. I used mapquest to plot from the house to a well known restaurant there called "Harbor House".
If you follow the directions to Harbor House, instead of stopping at the restaurant you would drive right past it and go until the road curves left. That whole area is a big parking lot. When the road curves left you should see to the right a walk-way and that is the access to the big beach. Park and walk that walkway and you will see many choices to stop and make your spot. A beach umbrella, beach towel, suntan oil, cooler with drinks, and goggles would be good stuff to carry with you. The path will take you past a public restroom and at that point you can take a left to the beach front. Most people go right and walk to the nice sandy areas. You are likely to pass turtles sunning as you walk. Pick any spot and enjoy. (Hint -- the further you go the less family oriented -- this used to be a nude beach). This is a massive beach and you can walk several miles before you know it!
The other beach at the harbor, instead of turning right as it says to "stay on Kealakehe Pkwy", continue straight. You will pass a small gas station and convenience store (did you need soda or sandwiches?) and also see many boats docked until you come to a parking lot (dead end) where people like to park and watch boats coming in (or sometimes whales and dolphins). Park in the lot. To the left you will see a small beach and probably people there with their towels and swimming. You walk across the rocks to the beach, enjoy.
See also our FAQ “Snorkeling, Where to Snorkel”
