As the boat glided down the Amazon River, I swung from a hammock and watched the seemingly endless jungle pass by. I was entranced; I'd never seen so many shades of green in one place. I had come to witness the Amazon rain forest firsthand, and it was already putting on an amazing show.

Commanding 2.3 million square miles, the rain forest is one of the most biologically diverse places on the planet, home to millions of species of plants, animals and insects, many of which have yet to be identified by scientists.

Thanks in part to the rubber boom of the late 1800s, it's accessible to visitors through a handful of port towns that dot the edges of a few of the thousands of rivers that weave through the jungle. One of the best of those towns for basing a visit to the Amazon is Iquitos, Peru — which, at more than 400,000 people, is actually a city. Aside from one highway that runs between it and a smaller nearby port town, there are no roads connecting Iquitos to the outside world. The only way into and out of the city is by plane or boat.

While most people opt for the under-two-hour flight from Lima or a daylong speedboat ride from a town reachable by car, I decided on a more uncommon approach to Iquitos: a three-day cruise via cargo ship.

I learned that cargo ships were an Amazon River basin transportation option from a German couple I met while traveling in South America with my husband. It sounded so romantic. We'd find a boat with room for us and spend a few days drifting along two tributary rivers before meeting up with the world-famous Amazon. Flanked by wild jungle, I would take in the first sights and sounds at a slow, relaxed pace. Thankfully, we're flexible travelers, because you can't book these trips in advance, and schedules are uncertain. Just traveling from the northwestern city of Trujillo, where we'd enjoyed some beach time, to Yurimaguas, the Peruvian river-port town from which the cargo ships depart, required a 20-plus-hour bus ride followed by a two-hour ride in a colectivo, essentially a shared taxi. (Most travelers get to Yurimaguas via the north-central city of Tarapoto.)

When my husband and I arrived in Yurimaguas, we went straight to the central market to buy supplies for the cruise: hammocks, and mosquito nets to drape over them; bowls for our meals aboard the ship; lots of bottled water; and snacks to get us by should the food look dodgy.

Then we headed for the port. The small dock, which could more accurately be described as a slab of flat shoreline that abuts the river, had enough space for a handful of boats. Using slats of wood as ramps, men carried armfuls of watermelons, bags of rice, furniture, electronics and live animals onto two docked cargo ships. Only one boat, the Kiara I, would let us aboard. (The Eduardo VIII docked next door had filled two entire decks with live chickens and wasn't taking on any human passengers.)

Finding a ride

We slipped onto the Kiara I and strung our hammocks on an open-air deck at the stern of the boat. This would be our sleeping area for the journey.

Then we waited. While cargo boats in the area regularly allow travelers passage for a fee (we paid the equivalent of about $30 apiece, which included meals), the cargo is the priority and the boat would leave only once the 200-foot-long ship was full. That, however, was a difficult thing to determine.

I had been warned that it could take a few days to embark, so this uncertainty only became a problem when we wanted to leave the ship to get lunch or dinner (meals were covered only when we were moving). I learned to study the cargo — if there was still a good amount of product to unload from a truck, it felt safe to leave the ship for a few hours.

To pass the time, I chatted with our hammock-mates. Of the roughly 50 passengers, about 10 were international travelers like us; the rest were locals.

Simply sitting on the docked boat was surprisingly enjoyable. At one point, a pod of dolphins splashed around our ship. We were also entertained by the nearby chicken boat. One by one, several chickens (presumably bound for the dinner table) jumped overboard. They bobbed away with the current of the river, prompting both cheers for the birds that were making a bid for freedom and a debate about whether chickens could swim.

By the time the boat left, we'd spent a total of 36 hours — and two full nights — on the docked ship. But once we got going, any frustration born from delay dissipated. The gentle, warm breeze and the sights and sounds of the Amazon made for a tranquil experience. Over the low rumble of the ship's engine, I heard a choir of birds and crickets.

Every so often, the green of the forest was broken up by stilted thatched houses. As the boat slowly passed, I glimpsed the lives of those who called the Amazon home: a young woman washing clothes, boys playing soccer in a field, young men loading bananas onto a long wooden boat.

The accommodations were pure cargo ship: Water pooled in parts of the rusty deck, and spiders came out in droves at night. I spotted a several-inch-long black beetle that sent me running. A Peruvian girl, who couldn't have been more than 5 years old, picked it up and moved it away without flinching.

The bathrooms were awful. The floor was covered with standing water. The toilet had no seat and didn't flush, so waste had to be washed down with a bucket. A pipe hanging from the ceiling in the middle of the room was used to fill the bucket. It also doubled as a shower, which I couldn't bring myself to use.

The meals were tastier than I expected, though a bit odd. One lunch consisted of chicken, rice and potatoes, while another was essentially the same ingredients but in soup form. For dinner, we were served a sweet, cinnamon-flavored milky soup with bits of floating rice. If you imagined a mug instead of a bowl, it would have made a decent after-dinner by-the-fire beverage. For breakfast, we were served chicken soup one morning and the milk soup another.

The journey continues

By the end of the second day, our boat reached Nauta, the small town that connects to Iquitos by road. Here, a lot of locals got off. A bus to Iquitos would take only about two hours, rather than the eight hours left to go via boat. Having gone four days without showering, the idea of getting to my destination more quickly was pretty appealing. But, after buying some beer and snacks, all the international travelers got back on the boat and gathered on the topmost deck above the wheelhouse. We weren't done with our journey.

Surrounded by strangers-turned-friends, I watched as the blue sky faded to oranges and pinks that deepened as the sun set. I had grown to appreciate how time seemed to move differently on the boat. The smallest moments and simplest observations were enjoyed in full, because we had nowhere else to be and nothing else competing for our attention.

Early the next morning, we drifted into the port at Iquitos. Groggy but excited to have finally made it, we exchanged contact information and went our separate ways.

Everyone on the Kiara I came from different walks of life, but on the ship, we were all equal. We were confined to the same space, ate the same meals at the same time and suffered through the same mosquito-filled heat together. It was a humbling reminder that we're all the same — no better or worse than anyone else in this world.

With traveling, we've made it easier to reach far-flung places, but I'm starting to wonder if we lose something when we jet around from place to place. Sometimes, I think the slow boat is exactly what we need.