Diamond Head Lookout, Honolulu

Diamond Head, a volcanic formation on Oahu Island in Hawaii, stands as the most frequented park in the state. In the 1800s, British soldiers mistook beachside calcite crystals for diamonds, hence the name. The site, also known as Diamond Head Lookout, provides breathtaking views of the Pacific Ocean and Honolulu, accessible via a trail leading to the crater's rim, formed about 300,000 years ago.

This landmark is part of the Ko’olau Range, a series of volcanoes that started forming underwater over 2.6 million years ago. Diamond Head's distinct crater, spanning 350 acres, emerged from a single explosive eruption, characterizing it as a 'tuff cone' – a specific volcanic formation.

At 762 feet above sea level, and 560 feet from its base, Diamond Head is a unique, monogenetic volcano, meaning it erupted only once. Its last activity was between 150,000 and 200,000 years ago, and it has been inactive since.

In 1905, the U.S. government acquired Diamond Head Crater and nearby areas, developing Fort Ruger, Hawaii's first military reservation, as part of coastal defense. Remnants of this military history, like Battery 407, Birkhimer Tunnel, and various defense headquarters, still exist.

Diamond Head Trail offers a rare chance to trek to a volcano's edge. This path leads to expansive views of Oahu, the renowned Diamond Head Lighthouse, a U.S. Coast Guard facility also featured on a postage stamp, and the Pacific Ocean. On clear days, even Molokai Island is visible.

The trail, established in 1908 for military construction, stretches 0.6 miles up the crater. It's a switchback path, originally made for personnel and mules carrying building materials. In 1940, the Kahala tunnel was added as the main entrance. Diamond Head was designated a National Natural Landmark in 1968.