Diamond Head is Honolulu's defining landmark — the broad, flat-topped volcanic crater that rises at the eastern end of Waikiki Beach and appears in virtually every postcard of the city. The 1.8-kilometre hike to the summit is steep but short, gaining 175 metres through switchbacks, concrete military tunnels, and spiral staircases built during the First World War. The view from the top across Waikiki, the Koolau mountains, and the Pacific is spectacular.
The hike takes 1.5 to 2 hours return and is suitable for most fitness levels, though some sections require ducking through low tunnels. It is popular: go early (before 8am) to avoid queues and heat. Reservations are required and can be made online through the Hawaii DLNR. Bring water and wear sunscreen — there is no shade for most of the route. Accessible from Waikiki by bus or a short drive.