By Eric Noland > Travel Writer

 Just after the turn of the 20th century, military strategists realized the value of Diamond Head, a volcanic ridge that soars at Honolulu's edge. Artillery batteries and an observation post were established at the top, so that this triangulation point could be used to direct fire at incoming hostile ships.

Its impotence was exposed in 1941, though, when Japan attacked Pearl Harbor from the air (and from the other direction). At about the same time, the development of radar rendered the triangulation post obsolete.

The trails, tunnels and staircases to the top still remain, and visitors are welcomed to Diamond Head State Monument - headquartered right in the crater of the old volcano - for an invigorating climb to the summit. It's eight-tenths of a mile one way, with an ascent of 560 feet, and there is no relief from the sun which quickly turns the crater into a Dutch oven, so it's a good idea to start early. Even at 6:30 one morning, we had plenty of company - seniors, families with young children, Japanese tourists with dressy footwear.

To the summit

There are two straight staircases, one infamously called 99 Steps, plus a metal spiral one in the observation tower.

But the reward for enduring them is considerable. When you crawl out through the camouflaged slit for the last short climb to the top, the view is spectacular. The green belt of Kapiolani Park, Waikiki Beach and Honolulu's thicket of high-rises stretch away to the west, while the Pacific has a deeper hue of blue from this height.

You'll snap a photo, of course - to get an inverse image of that postcard that sells so wildly down below.

Among the fishes

Hanauma Bay is another volcanic cone that lies just up the coast, but it contrasts sharply with Diamond Head's in that it's filled with water.

This has been Oahu's best snorkel spot since swimmers first donned masks and began peering beneath the ocean's surface. But there was a time 20 years ago when it was being loved to death. Tourists poured in daily, parking anywhere they could find a free spot on the dirt slopes above the bay. The beach was shoulder-to-shoulder - worse even than Waikiki. And the swarms of humans nearly outnumbered the tropical fish in the water. Folks trod on the coral, and fed frozen peas and squirts of Cheez Whiz to these wild creatures.

The city parks department ultimately stepped in and regulated visitation. Now, when the paved parking lot fills up, that's it; subsequent visitors are turned away. So it's wise to get to this place early, too.

The intervention is welcome, but the pendulum seems to have swung pretty far in the opposite direction, in that Hanauma Bay now has a Disneyland feel to it. Before heading down to the water, visitors are required to watch a film - ostensibly for educational purposes (don't touch the turtles, don't walk on the coral) - but it is more of a travelogue. You sit there in the dark looking at underwater footage of sights you'd rather be seeing out in the bay first hand.

And the money drip is continual: $1 to park your car, $5 to enter the park, 50 cents to ride the shuttle down to the beach, $1 to ride it back up, a staggering $5 for a locker for your personal items, more to rent fins, snorkel and mask.

The astonishing diversity and abundance of marine life in the preserve make all of this tolerable, though. Locals can't fish here, so the tropical fish grow to big sizes, and they are resplendent in their natural colorings - all the more so if you luck into a sunny day. You'll routinely see butterflyfish, surgeonfish, tangs, rainbow wrasses. Inexperienced swimmers will feel perfectly comfortable here, too, because a stout reef renders the inner bay bathtub-calm. Wade out to waist-deep, put on a mask and simply float on the surface.

The cliff road

Hawaii's highways tend to hug the coastline, because that's where the passage is easiest. But in southeast Oahu, Koko Head and the Koolau mountain range rise steeply from the water's edge, and the Kalanianaole Highway had to be cut along the flanks. Accordingly, the views from the road are sensational - black lava rock plummeting to deep-blue ocean, picturesque Makapuu Point, Rabbit and Turtle islands just offshore.

The around-the-island tour vans careen through here, providing, oh, five or so minutes at any given turnout. If you're touring independently, linger a while longer at the Halona Blowhole, and peer (or climb) down to the pocket beach at Halona Cove, where Burt Lancaster smooched with Deborah Kerr in the rushing shore break in the 1953 movie "From Here to Eternity." (In fact, it's now widely called From Here to Eternity Beach.)

Makapuu Beach is kind of a locals hangout, but it's a good spot for a picnic. Venture into the surf at your peril, though, as it is rough and unpredictable (as I learned on an ill-fated body-surfing experience a few years back, when I was tossed like a rag doll onto a submerged rock shelf).

Exclusive hideaway

There is some exclusive real estate along the Kahala Coast on the back side of Diamond Head. It was here that Doris Duke, a tobacco and hydroelectric power heiress, established a Hawaii retreat in the 1930s.

She called it Shangri La, and furnished the home with Islamic art that was the passion of her world travels. When Duke died in 1993, her will stipulated that the home be opened to the public on a limited basis. The Honolulu Academy of Arts conducts small tours, which originate at the downtown museum (you can't drive up to the mansion itself). At the heiress' hideaway, it's fascinating to peruse 13th-century prayer niches, ceramic vessels and textiles; a foyer where lights come on only if the sun goes behind a cloud; and a wall of windows that descends into the basement with the touch of a button.

This was one eccentric woman. Who else would build a 14,000-square-foot house with a boat moorage, a competition-length pool ... and two bedrooms?

Beat the crowds

Diamond Head Road skirts the mountain on its way from Kapiolani Park to the Kahala Coast. Few visitors seem aware that there is lovely stretch of beach just below the bluffs. Park in the turnout just up from Beach Road and nearby you'll find a paved pathway leading down to Kuilei Cliff Beach Park.

Where'd all the people go? We walked half a mile down the beach to Black Point, beyond which is the Duke mansion. Upon returning, a stroll in the other direction revealed a memorable view of the Diamond Head Lighthouse, brilliantly white and capped with a red dome, gleaming in the sun at the cliff top.

A few surfers and body-boarders were scattered about, but otherwise there were long stretches of open beach.

And to think that only a couple of miles away, Waikiki Beach was jammed towel-to-towel with tourists. Many of whom, no doubt, were at that moment pointing a camera vaguely in our direction.

eric.noland@dailynews.com

(818) 713-3681

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