Diamond Head, peak, 761 ft (232 m) high, along the rim of an extinct volcano, SE Oahu island, Hawaii. A prominent point in the Honolulu skyline, Diamond Head was designated a national natural landmark to protect its slopes from the commercial development along world-famous Waikiki Beach. U.S. Fort Ruger is at the northern end of the crater's floor. The crater was the site of an ancient Hawaiian burial ground.