When in Hawaii, this hike is a must.  It's relatively easy. It gets steeper as you get closer to the top.  Plus the steep stairs and the dark tunnel can be a little intimidating.  But they also add to the Diamond Head hike experience.  The best time to go is in the morning right when they open.  We got there before 7 and the parking lot was getting full.  Keep in mind that almost everyone that visits Hawaii will likely do this hike.  It was also a hot and humid day and so the early morning temperature was just perfect for the hike.  The hike is about 1.5 miles round trip.  It is paved in some parts and there are railings almost all the way up so this is a very friendly hike to all levels of hikers.  Make sure you bring some water because even though it is a very friendly hike, it is still a tropical climate and there is no water available once you go past the restrooms at the entrance.  

Once you get to the top, the view is just absolutely breathtaking and just a whole lot better seeing the view in person than in photographs!  From the summit, you get a 360 view which includes Waikiki, the city, the hill side going inland, and a whole lot of Pacific Ocean as far as the eye can see.  

For those wanting that extra challenge, if you are staying somewhere in Waikiki, you can probably run from your Waikiki hotel.  One of my morning jogs while in Hawaii started from Sheraton and ended up at the base entrance of Diamond Head.  That was about a 4mile round trip run.  Two more miles with a few hundred feet elevation and I could have knocked both a jog and a hike out in one day!