"The Amazon is both less and more than people imagine," expedition leader Carlos Romero says over breakfast on the first morning of our 10-day Lindblad Expeditions-National Geographic cruise into Peru's Upper Amazon.
"It is 'less' in the sense that people come expecting to see big animals like in a diorama," he explains, and 'more' because of the biodiversity and the interconnectedness of rainforest creatures great and small, including an estimated 2.5 million insect species. "There could be 10 million, we don't know."
It's easy to have expectations when we travel, even about the world's wildest places; they've been so David Attenboroughed and written about we can start to believe we know all about them before experiencing them for ourselves. I certainly arrived on this trip with a duffel bag full of ideas, all of which would be overturned by day 10.
The first surprise comes later that day. Putting on gumboots and insect repellent in preparation for a two-hour rainforest hike, I try to lower my expectations. But as soon as our small group sets off into the dense forest, our local guide dives into the impenetrable green beside the track, emerging moments later with a banana leaf – and on that leaf is a legendary bird-eating spider.
I can't believe my eyes, partly because a biologist friend back home had asked me to bring back a picture of the world's largest tarantula (which looks more than capable of crash-tackling a small bird, by the way). I hadn't expected to see one at all, let alone on our first day.
Walking on, we come eye to snake-eye with a young anaconda braided into the branches of a sapling. Then, hanging upside down in another small tree, there's a three-toed sloth with its ET-like face, reaching for a nearby branch in cartoon slow-motion with one long shaggy arm.
Seeing three iconic Amazonian animals on our first outing seems too good to be true, and it is.
Back on the Delfin II, the eco-luxe river vessel Lindblad charters for these expeditions, Romero explains why: this patch of rainforest is protected from poachers by resident caretakers (the local guides we'd walked with) who know it intimately.
"Anyone been in Galapagos?" he asks. More than half of us raise our hands. "Forget it. Forget about [blue-footed] boobies in the middle of the track. Here, you have to work to see the animals."
Sure enough, the next day on a longer hike in a different area, we see no wildlife. Instead we get up close and personal with some of the Amazon's 40,000 known plant species, first from above, by crossing a series of suspension bridges at canopy height, then at ground level where our onboard naturalists show us plants used for everything from treating diarrhoea to making blowguns.
The rainforest may be supermarket, pharmacy and hardware store to its human inhabitants (more than 20 million people live in the Amazon), but it has a dark side too.
"The jungle is very dangerous," says naturalist Rudy, but not for the reasons we expect. While you're keeping watch for jaguars – which are so rare he has seen only five in 40 years of living and working in the Amazon – an unassuming vine or tree will quietly do you in. Some are covered in spines like the porcupine tree, others exude toxic chemicals to defend themselves and almost all the plants we see are crawling with stinging ants and caterpillars.
After dinner that evening, with the Delfin II safely moored (tied to a tree on the riverbank), Rudy takes a few of us back into the forest for a night hike. It's humbling and disorienting, even before he asks us to turn off our torches and stand in the silent blackness for several long minutes.
You don't need darkness to feel disoriented by the Amazon, of course. It's so unimaginably vast, a few facts and figures will do the trick; 6437 kilometres long, it's the largest river in the world by volume and has 200 major tributaries, 17 of which flow for more than 1600 kilometres.
Travelling up and down two of those tributaries, the Maranon and the Ucayali, exploring the Pacaya-Samiria National Reserve (the largest protected area in Peru) that occupies the V-shaped space between them, enhances that sense of being spun around and not quite knowing where you are.
On day four, over celebratory pisco sours on deck, we glimpse the great Amazon, at the point of the "V" where the Maranon and Ucayali meet, but the newborn river of chocolate-milk swirls and eddies is rather underwhelming.
All week, in fact, looking out the cinema-screen window of my cabin at the muddy waters flanked by living walls of green, I can't shake the feeling that we could be in Cambodia or the Congo.
Getting out into the view on motorised open boats called skiffs helps me get my bearings. For one thing, there's nothing like a safari schedule to dial up the glory: morning mist rising from a satin-smooth river while a squadron of egrets flies overhead or, at the other end of the day, the warm wind in our faces as we speed back to the ship and the golden sun lowers itself into a horizon of trees, the air scented with wood smoke.
Then there are the stars of the show, New World monkeys – a troupe of squirrel monkeys swinging through the treetops or a howler lying along a branch like a man passed out on a couch – and birds so fantastic they could have flown from the pages of a Philip Pullman novel: unicorned geese called horned screamers, the pheasant-like hoatzin that swims and climbs better than it flies, a tree full of sleeping sand-coloured night hawks.
Halfway through the trip we get a chance to immerse ourselves more deeply in the riverscape. First by kayaking, an activity Lindblad pioneered on the Amazon as a way to tap into its peaceful side. Then, after lunch the following day, by taking a dip in a tannin-stained oxbow lake.
Who knew you could swim in the Amazon without being nibbled to death by piranhas? (The only sign of piranhas we see all week are necklaces made from their jaws at a village market; nor do we see any black caiman, thankfully, as these crocodilians can grow to five metres.)
Instead we swim with pink and grey river dolphins. They're not as sociable as their marine cousins, but we get near enough to hear them exhaling and see their small dorsal fins break the surface as we breaststroke through the black water.
It's a highlight of the trip for me and the only time I return to the Delfin II dripping wet, I realise later. I'd expected to be sweat-soaked and drenched by downpours on a daily basis, but the weather is surprisingly mild and there's no rain until day five. Then it pours.
On our last day on the river, a squall cuts short our morning skiff ride and develops into a storm, giving us an unscheduled "indoor" day to enjoy the Delfin II's delights: curling up with a book on a comfy white couch in the airconditioned lounge, massages in the small spa, dolphin-spotting from the open-air upper deck, gin and tonics in hand.
By mid-afternoon, however, cabin fever motivates us all to don waterproof ponchos and climb into the skiffs for the Amazonian equivalent of a rainy Saturday afternoon drive.
It's one of the best skiff rides of the trip. In my boat, naturalist Ericson enthuses about every sighting like a race caller – "Oh, my god! Look left, go up to that horizontal branch, along a little bit, there! Look at his be-you-ti-ful face!" – spotting birds with names even more colourful than their plumage such as speckled chachalacas, social flycatchers and, the last bird we see before heading back to the ship, panda-like white-headed marsh tyrants.
Back in Iquitos, with time to kill before our flight to Lima then home, there's one more surprise in store: the chance to hand-feed three young manatees at a wildlife rescue centre. Their skin is rubber-smooth, their snouts bristle with grandfather whiskers and their other-worldly mouths have side-fingers that gently grasp the water-lettuce leaves we hold out for them.
It's a fitting end to an expedition that has replaced all my preconceptions with first-hand experience of how the Amazon really is, this week at least. Because you can never truly know a place like this. So relax, and watch all the Amazon documentaries you like. They won't spoil a thing.
Qantas flies from Sydney and Melbourne to Lima via Auckland and Santiago, code-sharing with LAN. See qantas.com. Australian citizens don't require a visa for Peru.
Lindblad Expeditions' 10-day "Upper Amazon Aboard the Delfin II" trips run year-round and take up to 28 guests; cabins start at $8360 a person including return flights from Lima to Iquitos. See www.au.expeditions.com or call 1300 361 012.
Louise Southerden travelled as a guest of Lindblad Expeditions.