The shavenheaded Canadian with the eyebrow piercing is yelling over the roar of the boat's engine. His wetsuit is unzipped to the waist, and a little roll of babyfat poofs up over slick black rubber.

"I'd hate to have eaten a big tuna fish sandwich before this dive," he bellows to the other divemaster, his vowels all shaped in the curve of northern latitudes. I look at Chris, who has just eaten a fish sandwich. Fat drops of salt spray fly up from the bow of the boat, and I zip up my own wetsuit to stave off the cold.

"Or the big Mexican platter at John's," his colleague yells back. In fact, I have just finished a large plate of nacho chips, amidst some jokes about the wisdom of diving after a heavy meal. But I do not share this information with the men around me.

"So this is the kind of dive that might make you wake up tomorrow realizing you're that he-man diver you always wanted to be," the Canadian roars to us over the motor. "We'll actually be spending much of the first thirty minutes underground, in six different swim-throughs. It's a pretty strenuous dive. There's a part when we'll have to descend straight down, face-first, so take it slow and make sure to clear your ears."

As we slow and approach the dive site, I think: who wants to be a he-man diver? They often wear bikini swimsuits and talk incessantly about the features of their dive computers. I rarely hear them say anything about the sheer beauty of the marine world in which they are momentarily permitted to swim, or the mind-boggling reality that a vast and complex world is hidden just beneath the ragged bottom of our boat.

Chris says "I'm not really much for swim-throughs. I'll follow your bubbles on the top of the reef." The divemaster is momentarily perplexed by the idea that one of his clients would fail to chose the macho alternative, and he's further undone when I tell him I'll do the same. I have little desire to scrape the last remaining bits of age-old coral off the insides of an underwater cave just for the adrenaline it will confer. I'm still naïve enough to be excited by being able to hover underwater in the gargantuan shadow of the living reef.

Although Chris and I are the only people diving, the divemasters insist on doing the caves anyway. One of the divemasters is getting certified to lead groups on this area, they tell us, so he really needs to check it out. We're already convinced that these folks are a bunch of yahoos, so it doesn't surprise us much. We all roll off the back of the boat and start a gradual descent to the bottom. As the divemasters plod through their swim-throughs, Chris and I have ample time to savor the sensation of floating in an utterly alien (yet so amniotically familiar) atmosphere and observing the intense density of life around us. It is my last dive for now, and I feel utterly peaceful. My air stretches on and on. I hover in perfectly neutral buoyancy over the fractal forms of the coral. I move with certainty in three dimensions.

The divemasters emerge from one swim-through and head for another, a cave-hole in the reef. They signal us a question: do we want to follow them in or go up and over? Chris looks to me, and I tentatively signal up-and-over. I hate looking like a wimp, even under water. But in this situation, I do not look like a wimp: my signal is so half-assed that Chris interprets it to mean that I want to enter the cave. He goes in, and so I follow. The tube is just large enough to accommodate a diver and tank. It narrows slightly, rough stone walls falling in to either side, forcing me to hug the sandy bottom. The light dims. There's nothing to see anyway, but enfolding walls of rough stone. My breathing sounds unnaturally loud, a thick roar in my regulator. Light ahead: a vertical shaft, the exit. To get out, we must each rotate to avoid getting hung up on an overhang. I pause, fluttering my fins in a gentle reverse, as Chris negotiates the exit, then I too emerge from the hole and into the wide blue of the reef.

It is not over. The divers ahead are reentering another cave. This is the he-man part of the dive, I think, the part I will wake up tomorrow thinking about. I must maneuver until I am head-down vertical and allow myself to fall slowly, in gentle pirouette, down this shaft, my ears squeezing and popping the whole way. There is no coral inside the cave -- it has doubtless been sheered off by other careless divers in years past. I, too, bump and scrape my way down, into this dark trap, underground, underwater. I am not graceful. I wonder if I will panic, but have no idea if I will or not. I wait to find out.

Then the tube levels out, I see Chris' fins ahead and I'm soon emerging into open space. I zip up and catch Chris' fin. Up-and-over, I signal emphatically to him. Next time, up and fucking over. When the divemasters head into the next canyon, we two stay behind, holding position without moving at all, suspended in the clear water. I watch my exhaled bubbles make their long journey up to the surface above, like white jellyfish surfing a wave of carbonated fizz.

I am enthralled, at peace... and I'm feeling a little pumped from mastered the cave.