I'd always imagined that the entire Amazon region is covered in a canopy of trees so clotted with branches and leaves that the sun pokes through only in thin slants. That's certainly what it looked like from above — a pillow of emerald treetops cut through with a curving ribbon of water the color of a Hershey bar. Yet there I was, squinting even behind sunglasses, as I stepped out of the plane onto the tarmac of the Iquitos airport, deep in the Peruvian rain forest.

The Amazon River journey I took with friends offered other surprises, too. I'd headed there slightly panicked about possible dangers lurking in its waters and on shore. The nurse I saw at the international travel clinic before the trip had done nothing to discourage my paranoia, stabbing my shoulder with all manner of shots and arming me with malaria pills, a bottle of Cipro and a leaflet that spelled out the possibly fatal nature of Dengue fever, a tropical disease for which there is no vaccine. Yet, I would later stop taking my malaria pills. And I only smiled when, after we'd returned to Minnesota, one of my travel companions forwarded an Internet factoid about a man who got an infection from parasites who'd swum up his urine stream as he relieved himself off the side of a boat on the Amazon. Unlike me, she'd conveniently forgone the group swim in a tributary of the legendary river.

Iquitos is 2,000 miles from the Atlantic — the most remote inland port in the world — and is accessible only by plane or boat (most travelers fly from Lima). But it's hardly what you'd call sleepy. More than 400,000 people live in this city, and the main street is frenetic, with hundreds of merchants displaying their wares — coconuts, wigs, TVs, brooms, catfish — to the riders buzzing in and out of traffic on their motorcycles or motocarros, which are basically motorcycles attached to rickshaws.

That chaos dissolved the moment we pulled up to a dock on the edge of the city, where our home for the next three nights was moored. With only 12 guest rooms — each a harmonious blend of picture windows, modern lines and seriously high thread counts — the Aqua Amazon feels more like a country house from Dwell magazine than a cruise ship.

Launched in 2007 by a former Galapagos cruise company executive who wanted to bring luxury to the world's great rivers, the Aqua takes its guests up the Amazon and tributaries deep into the Pacaya Samiria National Reserve, a protected area in Peru that, at 5 million acres, is twice the size of Yellowstone.

Close-ups of wildlife

The first thing I noticed about the Amazon is that it's so wide it's difficult to make out the landmarks on the opposite shore. We were there in early November, which is considered the "dry" season, so the river was low and as still as a cup of coffee. As we glided out of Iquitos, cellphones went out of service. In fact, throughout the cruise, the only time I realized we were approaching anything close to civilization was when the crew rushed up to the deck to point their phones in the direction of stray lights blinking in the distance.

Days on the Aqua revolve around morning and afternoon excursions on two skiffs, each staffed by a driver, a naturalist and a medic. Our naturalists were Julio and Ricardo, who both grew up in the jungle and are passionate about preserving their region's ecosystem. Each is a bilingual encyclopedia of information, especially about the Amazon's birds.

For the entire first morning, the smaller rivers looked the same to me: brown water, vines, tree trunks, leaves, sky. But then Ricardo put his hand above his eyes and the skiff bumped to a halt.

"Oh, my, holay molay!" he shouted, before switching to a whisper so as not to scare off whatever it was he'd spotted. Slowly, I was able to make out something through all the green. There were storks, silver beaked tanagers, dusky headed parakeets, smooth billed anis and so many capped herons that we started to joke "Oh, you again" whenever a new one appeared. At one turn in the river, our group spotted six macaws sitting on branches, like ornaments on a Christmas tree.

We watched as sloths hung from high branches. Capuchin, red howler and black spider monkeys leapt from tree to tree. Neon blue butterflies flitted toward the water and then bobbed up toward the sky. We even spotted a capybara — the world's largest rodent, which looked like a rat the size of a boar — sniffing along the shoreline. The famous pink Amazon dolphins were also frequent companions, although I didn't find them enchanting. Their flesh-toned humps looked to me like wads of already-chewed bubble gum.

The combination of the heat, the sun and the sensory overload of so much new scenery meant that most of our group napped between lunch and the afternoon expedition. There were very few bugs during the day — the staff of the Aqua convinced us the malaria pills were unnecessary — so many of us spent our siestas lounging on the deck, shaded by enormous white umbrellas that seemed to float above the ship. I usually headed to my room, opened the curtains and watched the shore pass by from beneath cool sheets, lulled by the gentle current created by the ship's motor. I doubt I was more relaxed in my mother's womb.

Evenings were devoted to extraordinary meals, the Amazonian equivalent of farm-to-table. We feasted on hearts of palm tofu with armored catfish caviar and braised short ribs in molasses and masato, a type of Amazonian corn beer. We drank pisco sours and pink cocktails made from the extremely sour camu camu berry. One night the setting sun shot magenta streaks through a navy blue sky.

We broke that pattern to take one evening expedition in the skiffs. Julio and Ricardo guided the drivers through the black night, holding spotlights above their heads.

Then the sound of "Oh, my, holay molay!" rang through the air. Ricardo had spotted something. But what?

Our skiff pulled up to the shore.

"There's something in the sand," Julio announced. "Elizabeth, can you see it?"

I could not.

"There," he pointed, dumbfounded by my blank stare. "There."

"I can see sand," I said. "But nothing else."

It was at this point that Moises, our twenty-something medic, pulled off his shoes, rolled up his pants and leapt off the front of the skiff. He reached into the sand, and after some wriggling, pulled up a caiman by the neck. It looked at us, clearly startled, probably traumatized, before Moises released him into the water.

The 'lungs of the world'

Even though the mission of the Aqua is to create an awareness and understanding of the crucial importance of a region that has been called "the lungs of the world," the crew also took pains to remind us that while we were technically in a nature preserve, we were also floating through the home of 30,000 people, who according to Julio prefer the term "river people" to Indians. Families in sun-bleached T-shirts and track shorts putted by in motorboats made from hollowed-out logs. They live mostly by fishing, hunting and farming, not to mention making and selling crafts to tourists.

Villages are mostly made up of thatched huts on stilts, some equipped with satellite dishes. Many are swallowed by the river during the rainy season, only to be rebuilt when the skies clear. In one village more than three hours from where the Aqua was moored, Ricardo introduced us to the head of the local PTA, who cheerfully accepted what suddenly felt to me like a pathetically small gift of notebooks, pencils and crayons.

On our last full day, Ricardo and Julio stopped the skiffs at a bend where the river was as dark as heavily steeped tea. This "black water" is highly acidic, and according to Julio and Ricardo, less prone to bacteria than the sediment-rich waters elsewhere in the Amazon.

"We can swim here," Julio said.

I don't think any in our group would have felt the need to jump into what amounted to a mucky hole if it was in the United States. But we were in the Amazon. Shouldn't we give it a go?

Several in my gang didn't think so. We'd fished for piranhas the day before and saw how eagerly they jumped at the raw meat dangling off our hooks. What if there were caimans, not to mention parasites?

It was in the middle of this indecision that Moises did a round-off backhand spring into the water.

And that's all it took for a few of my companions to join him.

So I tiptoed in. The water was warm, as I had expected, but refreshing, too.

"Go under," Julio instructed me.

"But I don't want to get sick," I said.

"You won't," he answered.

Knowing I'd be in Minnesota the next evening, I looked around, willing myself to remember the scene unfolding in front of me. What had just days ago been a wash of leaves was now a mosaic of hundreds of shades of green, from lime to avocado to neon to khaki. It was unlikely I'd ever see this perfect speck of the world again.

While some might argue that floating wealthy people through one of the globe's most endangered and poor regions is in questionable taste, it's equally true that these cruises have helped thousands understand on a visceral level what's behind the headlines. It would be impossible to disembark and not be in some way changed.

"Go under," Julio shouted from the shore. I didn't know at the time that none of us, despite not taking our pills, would get malaria. Or a parasite or, in my case, even traveler's diarrhea. The truth was that in a very short time we had all come to adore Julio and Ricardo and Moises and the rest of the Aqua staff. I trusted that I'd be OK.

So I dove down, and pulled my way through the dense water until I could no longer stand. When I surfaced, one of my friends was laughing. She'd ventured much farther from shore than the rest of us. And now, at the tail end of a trip filled with once-in-a-lifetime experiences, she was swimming less than a yard from a pair of bubble gum pink dolphins that had come over to check us out.

Elizabeth Foy Larsen is the author of "Unbored: The Essential Field Guide to Serious Fun." She lives in Minneapolis.