When the Judas Goat arrived, most of the invasive goats on the island were already dead.

Like an undercover informant bringing down a crime syndicate, he infiltrated their hideout. Pumped up on hormones the other animals couldn’t resist, he attracted a crowd. With his horns painted in bright colors to make him easy to spot, he drew the others into an open clearing, where trained snipers were waiting on land and in helicopters. The men brought them all down with biodegradable bullets and left the corpses to decompose.

After this story played out a few times, the Galápagos Islands of Santiago and Isabela, off the coast of Ecuador, went from having 100,000 destructive goats to being goat-free in 2006, and have stayed that way. Even if one Judas Goat went rogue and hid, there was a solution: His tracking device could be set remotely to self-destruct.

The people who run the Galápagos National Park system are very serious about keeping these pristine islands in a natural state. I’m humbled and impressed by the limited impact of humans in these primal areas, where nature still claims the land as its own. Tourists only step on 0.001 percent of the land set aside as a national park — and the national park is 97 percent of the total land mass. On some islands, nobody comes ashore except scientists with fumigated clothing — underwear included.

It’s hard to believe how completely nonplussed the Galápagos animals are by us humans until you see it for yourself. The sea lions just yawn when someone gets in their face with a camera, and the sea turtles barely alter their course when they are headed toward snorkelers in the water. The giant land tortoises, which can surpass 500 pounds, just munch on grass and ignore us, not even bothering to retreat into their shells. With no history of predators, fear is just not in the animals’ DNA.

One morning we wade in the water on a secluded beach as rays swim in the surf and a heron almost as tall as me ambles by, bored with the silly humans. A baby sea lion about a month old emerges from the water and looks us over. She smells a few tourists’ toes, bleats as if to say hello, then saunters back into the water, satisfied.

A cruise through the Galápagos Islands is not about onboard shows and dining buffets. In fact, the big “floating hotel” cruise ships are banned altogether. Most ships carry between 14 and 42 passengers, though a few are bigger to accommodate whirlpools on the deck and larger cabins. The smaller vessels are able to navigate deeper into bays, while those with powerful engines can go farther and faster.

Here it’s not really about the facilities, anyway — it’s all about the animals. One morning, it’s sea lions and colorful Sally Lightfoot crabs; that afternoon it may be land iguanas and penguins. On some shore stops, the ground is a moving mass of sunning marine iguanas, like miniature dinosaurs that seem to be sneezing as they separate seaweed from the ejected seawater. It’s not uncommon to see a plume from a whale’s spout as your ship moves from one island to another, or porpoises providing a lunchtime show off the bow.

The bounty of nature on the Galápagos is staggering, with giant tortoises and frigate birds mixing it up with pelicans and blue-footed boobies. All find plenty to eat in the fountain of life created by the Humboldt Current and local climate conditions here on the equator. Besides the fish, the crabs are the only creatures worried about predators, so they’re the only ones that scurry away. When we approach a beach on Española Island, the sand appears scattered with boulders. As our small boat gets closer to shore, however, we see some of those boulders moving. They are really hundreds of sea lions sunning on the sand and rolling in the surf.

With these islands cut off from the mainland and other islands, evolution is on display in a way no classroom can convey. So is the power of Earth’s shaping forces. As we follow the path on Isabela Island’s Urbina Bay, we see shells and coral heads on the ground after walking five minutes inland from the beach. “This area used to be underwater until 1954,” our guide explains. “The shoreline moved out one kilometer after volcanic activity made the ground rise up. People who landed here soon after found decomposing sea animals in this area.”

At Punta Moreno, I’m glad I’ve heeded the advice to bring sturdy shoes with thick soles as we spend most of the time walking on lava rock that flowed like liquid from Cerro Azul volcano a few hundred years ago. In some parts the lava rock looks like rope, in others it looks like an asphalt road that is cracking in the heat. The limited vegetation here stands out, as do the pink flamingos attracted to the lagoons.

Right off the shore it’s a different story, however, as we don wetsuits and snorkel with penguins, turtles, a giant manta ray and a rainbow of fish. The exercise is a welcome offset to the hearty lunch that follows, a bounty of ceviche, bacon-wrapped filets, three vegetables and fruit salad. In the afternoon we board small boats to venture into the mangroves nearby. It’s another cornucopia of wildlife, with golden rays and penguins in the water; pelicans, cormorants and boobies moving between water and land.

The company I am sailing with, Angermeyer Cruises, has an impressive list of procedures in place to limit man’s impact. A desalinization machine on board supplies the water, and guests refill reusable bottles with what’s purified here. Biodegradable soap and shampoo are in the cabins, and bottles are the reusable ones. Nothing goes onto the islands and nothing comes off them; and as some tourists have found out the hard way at the airport, that includes pebbles and sand.

After a week of exploring islands while being confined to a rocking ship each night, a few days in Quito at the end of the Galápagos trip provide a nice contrast. Instead of trying to hold off the march of man, Quito is a study of what man has left behind from the Inca age through the present.

Quito, the first designated UNESCO World Heritage City, boasts 16th-century architecture built at nearly 10,000 feet above sea level, framed by peaks that are frequently topped with snow. Once a major Spanish outpost, the historic center is a delight of narrow streets, church plazas and stately buildings that predate the U.S. Jamestown settlement.

If you want to see the whole city laid out before you, ride the telefériqo cable gondola 2,000 feet higher. It whisks you up the slopes of Mount Pichincha, with great views of the valley and surrounding mountains.

The altitude can be taxing even at the bottom, but thankfully the old city center is compact and suited for casual strolling. I drift among churches so gilded and detailed on the inside that it’s hard to keep my eyes from being completely overwhelmed. Here the Spanish Crown’s wealth is visibly on display, with intricate altars covered in gold and stone carvings that took generations to complete.

This central part of Quito has returned to its former glory after decades of neglect and is now one of the most attractive historic centers in Latin America. It once again feels like the heart of the city, the main plaza buzzing with people and the restaurants hopping. Sundays are the best day to take it all in, when many of the streets are closed to cars and are filled with pedestrians and parades.

As I board a plane to head home after exploring both the domain of beasts and the domain of man, I am moved by the wealth of beauty and richness in this ancient land on the equator.

Info To Go

International airlines fly into Quito (UIO), and there are internal flights to the Galápagos. Galápagos trips are available through major international tour companies such as Geographic Expeditions or local companies such as Angermeyer Cruises and Metropolitan Touring. All 86 ships registered to ply these waters make the same stops; base your decision on the kind of ship, your budget and the number of days. Factor in $110 in national park fees not included in the price.