The volcanic tuff cone on Oahu known for its hiking trail and panoramic views is Diamond Head.
Known to Hawaiians as Lēʻahi, Diamond Head is an approximately 200,000-year-old volcanic cone overlooking Honolulu and Waikīkī. It formed from explosive eruptions that deposited layers of ash and other volcanic material, which later hardened into tuff. The crater’s distinctive profile makes it one of Oahu’s most recognizable landmarks.
The popular summit trail was built in 1908 as part of the U.S. Army’s coastal-defense system. It climbs from the crater floor through steep paths, stairs, tunnels, and former military installations before reaching viewpoints over Honolulu, the Pacific Ocean, and the island’s southeastern coast.
The English name arose in the nineteenth century when British sailors mistook calcite crystals on a nearby beach for diamonds. Diamond Head became a U.S. National Natural Landmark in 1968. Koko Head and Punchbowl Crater are also volcanic features on Oahu, but neither is the tuff cone identified by this question.