Diamond Head Crater is one of Hawaii's most famous landmarks and the hike to the peak is a must-do when visiting O'ahu. The trail is short, but steep and varied, including paved path, switchbacks, a tunnel and steep stairways. You are rewarded with panoramic views at the top. The trailhead is accessed at the Diamond Head State Monument. Hours are 6 a.m. to 6 p.m. daily. The last hikers must start up the trail by 4:30 p.m. The trail is exposed so bring plenty of water and sunscreen.