If you're looking for a more strenuous workout, begin your hike from parking lot fronting the Waikiki Shell. Every Saturday, the Hawaii Clean Air team organizes a hike with the Shell as a starting point. If, on the other hand, you are pressed for time or don't want to overwork yourself, you can drive into the crater via an access tunnel and begin your hike from there. That option will save you about 45 minutes to an hour of road walking.
As I mentioned earlier, the trail up Diamond Head is used extensively. Consequently, if you're looking for solitude and being one with nature, look elsewhere.
The hike to the top will take about 30 minutes or so. Be prepared for a breath-zapping ascent up a stairwell from hell (the number of steps is well known by Diamond hiking enthusiasts). Also be prepared to travel through a tunnel system that could be quite daunting for those who are afraid of the dark or are claustrophobic. Here's a hint: bring a flashlight or tag closely behind someone who has one.
At the top, you'll scramble through an abandoned bunker to a extraordinary view of Waikiki and the beautiful waters off of it. Pack a lunch and something to drink and you can spend some time enjoying your meal with a view that no restaurant can match. And if you didn't bring anything to munch on or to drink, you can always purchase something from Hare Krishna followers who are known to sell (they call it "accepting donations") soft drinks and snacks at makeshift trailside vending stands.
In the latter part of 1996, Wing Ng, a trail club veteran, told me about several access routes to the crater rim from various ridges and slopes on the outer crater. He even did a write-up about these routes.
What's more, Wing told me about a trail that jogs around the crater rim and as of mid-November 1996, I've done this circle route twice. Overall, the trail is quite pedestrian and save for a couple of narrow, rocky sections where the crater rim overlooks La Pietra School and Kapiolani Park, it's easy do-able in two to three hours.
Whatever route you take, try the Diamond Head hike particularly if you're a visitor to Hawaii, for you'll enjoy a decent workout and beautiful views without spending a dime.