Dropping into the head of the canyon, we were instantly engulfed by tunnels of vegetation, one after another, sometimes wading through the water, sometimes balancing along a latticework of deadfall suspended like a bridge above the streambed. When the brambles became impassable, we would scrabble up the canyon sidewalls and work our way along slopy, discontinuous ledges.

Slithering, clambering, and clawing through bush—literally bushwhacking—is unique to Blue Mountain canyoning. To be a good canyoneer here, you must be a great bushwalker. It was instructive to watch how gracefully Rick and Derek tiptoed along the alligator backs of giant logs, contorted through cobwebs of vines, and leapt from rock to rock. We were as efficient as guerrillas, the man in front rotating as each of us ran into vegetal cul-de-sacs and advised the two behind to find a different path. At any drop, or whenever we got rimrocked, the point man would already have a rope ready by the time the other two arrived.

We were down in the dark, passing from one chamber to the next, when suddenly, right in front of us, there was sky. A brilliant wedge of blue between two massive black walls. At our feet, the stream rushed toward a drop-off, pooled in a cleft as if psyching itself up, and then slowly slid over the edge like a suicide jumper who has second thoughts a moment too late.

We took turns stepping carefully to the lip, hanging onto a limb, and looking down. It was a tremendous drop. The rock was undercut and the stream came apart as it fell through the yawning emptiness.

A hundred feet down and to the right was a long ledge. Unfortunately, below that point we could see nothing but blank walls.

"She may not go," said Rick. "After the ledge it's a hell of a long ways to the ground and looks like there's nothin' for abseils."

I volunteered to check it out. Reaching the ledge required traversing a fragile trellis of branches suspended in space—something akin to crawling out onto a lilac bush drooping off the side of a 50-story building—which I managed, barely. On the ledge I hung out as far as I could in different places, searching the walls directly below. Unless I found something from which to set up another rappel, I would have to jug back up the rope and we would be forced to somehow back out of Bennett Gully.

I was about to give up when I spotted something beautiful: a dead tree. A slender, limbless, blackened trunk leaning out of a seam. I immediately rappelled down to it and attached myself. I was now two ropes below Rick and Derek.

"It'll go!" I yelled up, exhilarated.

Rick's voice was barely audible. "Will...the...ropes...reach...the...bottom?"

When you're looking straight down, it's hard to judge distance. I studied the surrounding cliff faces disappearing into the forest. Our ropes were 200 feet long. It couldn't be more than 200 feet to the bottom.

"Ye-e-e-sss...."

I wasn't sure. I thought they would reach. It was a judgment call.

"Abseiling!"

Rick and Derek rapped down to the ledge, pulled the ropes, set up the next rappel, and started down again.

The one foolproof way to get yourself killed in a canyon is to get stranded halfway. If it starts to rain, you'll either be drowned, swept over the cliffs, or die of exposure. Even if it doesn't rain, but you're wet and the temperature drops, or the wind picks up and blows the waterfall over you and you subsequently become wet, you'll be popsicled in a matter of hours.

The one foolproof way to get stuck halfway is to pull your ropes down from above, eliminating all chance of retreat, only to find that they don't reach the bottom. Unlike in mountaineering, where you can usually turn around at almost any point, serious canyoning is a one-way trip. Once you pull your ropes, the only way out, the only way back home, is down.

Derek and Rick completed their descent and again pulled the ropes. Then we were all three hanging from a small dead tree on a remote cliff-face in the middle of the Blue Mountains. We knotted the ropes through the sling around the tree and dropped them.

They dove down through space, and stopped. They didn't reach. I couldn't believe it. We could see the ends dangling in midair, snapping lazily like tiger tails, the forest floor still somewhere far below.

"They're really close," I said.

"Fair dinkum," said Rick. "We get down there and we'll be laughin'."

Derek chuckled.

"You have the extra short rope, right, Rick?" I was trying to sound imperturbable. They knew what I was about to suggest: tie the short rope permanently to our dead tree, put a loop in the end, and hang the long ropes through the loop. It would require a midwall transfer from the fixed rope to the double, a dangerous maneuver at best, but it would give us an extra 30 feet or more.

"Tricky," said Rick, obviously pleased.

"If it doesn't reach—" Derek shrugged and didn't finish his sentence.

We rerigged the ropes, and I went first. Down the single line, making the transfer onto the double; then came a great swing out into midair several hundred feet above the earth, something that always gives one a minor synaptic shock. As I slid down the ropes, 15 feet out from the overhanging wall, I still couldn't tell if they reached the ground. Near the bottom the ends were coiled in the top of a tree. I anxiously descended through the tree to the very end of the rope. I was ten feet from the ground.

Close enough. I dropped.

"The....ropes...reach!"

Derek let out a battle cry and swung into space.

When he reached the ground, Rick, laconic as ever, looked back up and said, "That dead tree. Won't be there for long."

By twilight we were walking through tall grass between ghostly blue gum trees. It began to rain, and Rick and Derek start singing "April Showers," the Al Jolson tune. Then a cold night set in and it began to pour.