We see them before we hear them and then hear them before we see them. The billow of spray from the astounding, three-kilometre-wide Iguassu Falls on the Argentine-Brazil border appears as nature's white veil from our plane.
Later, approaching through the Brazilian rainforest, the visceral roar of one of the world's new seven natural wonders shakes the spray-soaked ground, long before we see it. And finally, we feel them as we teeter on a flimsy walkway in the maw of La Garganta del Diablo or Devil's Throat.
At this watery epicentre, we're circled by 260 degrees of raging falls in an 82-metre-high, 150-metre-wide and 700-metre-long U-shaped chasm. They say your life flashes before your eyes at such moments, however, it's a battle just to keep your eyes open as spray whips off the water, completely drenching the hardy folk who have donned plastic ponchos to walk to the centre of the water.
It's a primeval moment of accepting one's human vulnerabilities. What if the powerful rage of water – up to 12,743 cubic metres a second – takes out the walkway pylons? It's a long way to drop. And what's that in the river below the falls – crocodiles? Naturally.
Best to concentrate on the absolute majesty, and the spectacular rainbow that wraps around Devil's Throat like a ribbon. It's formed by the refraction of light against mist. One also has to wonder how many cameras, mobile phones and wavering selfie sticks have slid into the devil's maw.
Nature has taken a greedy chomp out of the basalt landscape, leaving Iguassu's serrated, semicircular flourish of 275 separate falls set in World Heritage-listed subtropical broadleaf rainforest between Argentina, Brazil, Paraguay and Uruguay.
Here you find the largest single protected remnant of the Paranaense subtropical rainforest, which belongs to the Interior Atlantic Forest. This forest biome that historically covers parts of Brazil's east coast, northern Argentina, Uruguay and eastern Paraguay, is renowned for its rich habitat and species diversity.
There are more than 2000 plant species, 400 bird species like the tirica, black-fronted piping guan, harpy eagle, great dusky swift, vinaceous-breasted amazon and toucan, and as many as 80 mammals including the broad-snouted caiman, giant anteater, ocelot, jaguar and jaguarundi.
But sometimes the largest creatures in the forest are the least dangerous. As we make our way down the falls path to Devil's Throat, I'm more concerned about Lonomia obliqua, the world's deadliest caterpillar, whose venom causes severe bleeding, followed by death.
They're difficult to see and gather in larger numbers on the bark of trees. The centre of the slippery, narrow falls path is where I'm staying, also slightly spooked by the aggressive little coati – members of the racoon family – that have been known to attack tourists for their food. Alarming signs bearing graphic images of bloodied, savaged hands pop up here and there.
But the world's great natural wonders often come accompanied by a frisson of danger, even if it's simply a salutary reminder of our insignificance.
There is a kind of waterfall rivalry between Iguassu and the Victoria Falls that separate Zambia and Zimbabwe. Iguassu is almost twice as wide, but Victoria is considered larger because its water curtain is less interrupted by islands and rocky outcrops.
Both are giants compared with, say, Niagara Falls on the Canadian-US border. Former American first lady Eleanor Roosevelt, on seeing Iguassu, exclaimed, "Poor Niagara!" Iguassu is four times wider than Niagara.
It's been a long day, but worth it. Our group left Buenos Aires at 6.45am for a two-hour flight to the north-eastern corner of Argentina in the Misiones Province, before driving across the border into Brazil.
This is where the Iguassu River, after a 1320-kilometre journey, drops dramatically, before flowing another 23 kilometres to lose itself in the Parana River.
Iguassu is part of our Captain's Choice private jet three-week tour of South America, visiting Argentina, Brazil, Cuba, Panama, Ecuador, Peru and Chile's Easter Island. A downgraded runway in Brazil means we must first land in Argentina and then bus to Brazil, where you get the full frontal, panoramic views.
Iguassu presents wonders at every turn. Such as clouds of multicoloured butterflies dancing around our heads. Or bursts of colour from trees like the cockspur coral tree whose bloom is Argentina's national flower.
After Devil's Throat, Captain's Choice has organised a treat – a picnic overlooking the first giant drop of falls, which are as white and solid as a glacial curtain. Glasses of Dom Perignon and caipirinhas, then a loaded table of salmon, fruit, stroganoff and potato gratin greet us.
Finally, the piece de resistance – our choice of adventures – mine is a scenic helicopter flight where Iguassu's majestic geology is revealed. Others choose the Macuco Safari Boat trip, which roars upstream to the base of the falls. We've already heard the shrieks of terror rising through the air as the boats brave giant waves.
Others visit the Iguassu Falls Bird Park where great aviaries display the forest's toucans, crested cranes, boa constrictors, turtles and iguanas.
At 6pm we're Flying Down to Rio, with apologies to Fred Astaire and Ginger Rogers' 1933 movie. And like movie stars we're offered more champagne, Argentinian malbec and a dinner whipped up by our onboard chef. Fantastico!
Captain's Choice Discovery of South America is a 22-day journey by private jet from Sydney to Buenos Aires, Iguassu Falls, Rio de Janeiro, Havana, Machu Picchu, Panama City, the Galapagos Islands, Cuzco and Easter Island. Departs Sydney on August 23, 2018, and is priced from $89,500 a person twin share.
Alison Stewart was a guest of Captain's Choice.