We've rafted the Shotover and the Sun Kosi, canoed the Zambesi and cruised the Danube - but even those wonderful river trips didn't have the combination of scenery, history and adrenaline provided by whitewater boating on the Colorado River through Arizona's Grand Canyon.
Judi and I, well into our late 60s, did grumble a bit about the ungainliness of clambering into the eight-passenger, outboard motor-powered pontoon boat perched on the edge of the fast-flowing but flat and otherwise benign-looking muddy-brown river, reached after a heart-stopping bus drive down a steep and winding dirt road to the floor of the 1.6km-deep canyon.
But embarrassment was quickly forgotten as we and our much younger American shipmates were raced around a corner and into the first of a succession of swirling and foaming whitewater rapids.
"Hang on tight like I told you," shouted Cole, our Hualapai Indian guide and driver. "First one up's a doosie."
A doosie? It was a douser, a surging, racing, whirling mass of brown and white foam into which our craft plunged and bucked. Water, masses of it and cold, rose from the V between the twin bows, loomed over us and crashed down, battering, drenching and chilling.
We were to stay soaked to the skin for two more thrilling hours as, buddy boat close by, we battered our way through a succession of huge rapids, including one that Cole said dropped us 5m in a few seconds. My eyes were closed for most of that one, white knuckles clinging desperately to the safety rope beside my hips.
"Always lean in, not out," Cole had said. "That way, if you fall, you fall inside the boat." His good advice was well taken by Judi, who did lose her grip on one big rapid, but fell forward into the water-filled bottom of the boat rather than into the river and emerged laughing with relief.
Sometimes, said Cole, they did lose a tourist into the water. But retrieval, he promised, was a well-rehearsed and relatively simple manoeuvre. Once, most embarrassingly, a driver lost his grip and was dunked, leaving the buddy boat driver to fish him out and a passenger to take over his tiller.
The 20km rapids section of the river trip passed in a flash. There was little time between rapids to take in the canyon itself; we were flat-out hanging on and surviving.
But the adrenaline rush was only part of the experience. This is the Grand Canyon, described as the world's most spectacular example of the power of erosion - a chasm 443km long, up to 29km wide and 1.6km deep that has taken between three and six million years to form. The powerful forces of the rushing river, of rain, snow, heat, frost and wind, go on sculpting and melding the fantastic shapes of precipitous bluffs and towering buttresses.
After the rapids, we drift leisurely along on the 45km flat section of our five-hour river ride, and look up from the river - straight up, almost, 1.6km to the top - at wall after sheer wall, buttress after buttress, cliff, canyon, arroyo, gulch; colours too, browns, golds, red, white; curves and contours. Above it all, a narrow band in the distance, is the clear cobalt-blue Arizona sky.
We and our fellow passengers, Americans all, are simply awed.
It's hot down here, now that we've dried off somewhat under the noon September sun, but there's a cooling effect from the river, 150m wide and running quite quickly.
We have a sandwich lunch on the river in the shade of a towering bluff. There's a beautiful waterfall up a side canyon to visit, and we scan the canyon walls for cougar and big-horn sheep. We see neither, not even near small patches of wild tobacco which the sheep like to browse.
This place was once Indian territory, and the Hualapai tribe has the concession to run the river trip we're on.
The Hualapai Nation originally lived on two million hectares. Its 2100 members now have a reservation of 400,000ha that includes 160km of the Colorado River and south rim of the Grand Canyon.
It owns and operates Grand Canyon West, a commercial tourist operation whose facilities include the much-hyped Skywalk, a vertigo-inducing, horseshoe-shaped, glass viewing platform jutting out 1430m above the canyon floor and popular with tour groups from Las Vegas, three hours by road or 30 minutes by helicopter to the west.
We spot helicopters everywhere as we prepare to beach at the end of our river trip, just a few miles upriver from the Skywalk. I count 12 in view as they ferry tourists from Las Vegas. It's a sophisticated operation, with its own air traffic control system, one far removed from the tranquillity we've just experienced.
That's how we leave the riverbank - in another burst of adrenaline - in a natty, five-passenger chopper that whisks us straight up the canyon wall to civilisation. Talk about the icing on the cake.
What to do: The Hualapai River Runners trip operates from mid-March until October 31 each year.
Where to stay: Hualapai Lodge.
Robin and Judi Charteris paid their own way to North America, but experienced the Grand Canyon as guests of Hualapai Tourism.