From Wikipedia:  Diamond Head is the name of a volcanic tuff cone on the Hawaiian island of Oʻahu and known to Hawaiians as Lēʻahi, most likely from lae 'browridge, promontory' plus ʻahi 'tuna' because the shape of the ridgeline resembles the shape of a tuna's dorsal fin.  Its English name was given by British sailors in the 19th century, who mistook calcite crystals embedded in the rock for diamonds.

Diamond Head is estimated to be about 150,000 years old and extinct for 150,000 years.  The eruption that built up Diamond Head was probably very brief, lasting no more than a few days. It was probably explosive, since when the cinder cone was originally formed, the sea level is thought to have been higher and the vent burst erupted over a coral reef. Another factor probably contributing to the eruption's explosive nature was that rising magma would have come into contact with the water table. The eruption's relatively brief length is thought to explain why the cone today is so symmetrical.

Naturally, Doug has put a microwave antenna up there somewhere.

Here's where we're going.  That sure does look like a long and winding road.

So let's take a leisurely stroll up to the top.  This path is on the back side of Diamond Head, away from Waikiki.

Note how the arrow points "up."

And up we go.

And up and up.  You'd be surprised just how many tourists are willing to make this trek.

There's a nice view.  We're looking away from Waikiki here.

This aerial view from Wikipedia gives a better picture of Diamond Head crater. 

Here's an old winch that was used to haul up ammunition for the gun emplacement on top of the mountain.

Bill poses.

Are those steps up there?

Yep.  With more to come.

This place is getting downright crowded.

Now that we're nearly winded, we've arrived at a serious set of steps.  A hundred and fifty-seven of them.  Bill took the steps up while Doug went the long way around on the "easy" path.  Yeah, "easy," right.

Doug and his friend prepare to make the final push to the summit.  Doug will make it.  Not so sure about his friend.

Bill looks back down the steps he just climbed.  And then he puffs a little.

So this is the Diamond Head gun emplacement...  Doesn't look like it's used much anymore.  Actually, the bunkers we’ve come to see are all part of Fort Ruger, which served as the first military reservation in the Territory of Hawaii. Named after Civil War General Thomas H. Ruger and built in and around Diamond Head Crater, the fort was established by the United States in 1909 for the purpose of defending the harbor of its newly annexed territory.

Oh boy, more steps.

Round and round we go.

Now we're inside a bunker.  There used to be a gun mounted on that pedestal, I think.

You shoot through the slot.

And a narrow slot it is.

Here's how you get out of the bunker.

And here's the view from above.   Those are some mighty Ritzy hotels down there.

Throngs of tourists take in the view.

Doug once installed an internet connection for the Coast Guard commander who lives in the house by the lighthouse.  Doug even got to go up in the lighthouse on a tour.

And there's Waikiki.  See the little pink Royal Hawaiian down there in the middle of all the high rise hotels?

See it better now?  It used to be the Queen of Waikiki Beach, but now it's dwarfed by ugly old high rises.

Bill likes the view.

Look!  Another bunker over there.

Take it all in while you can, Bill.  You're not likely to be back up here for quite a while.

In fact, Doug says this will be his last trip.  I guess if you've seen one view of Waikiki from Diamond Head, you've seen 'em all.

Time to go back down.  This time Bill will take the "easy" route and Doug will take the steps.

Oooh, a tunnel.

Bill had fun.