Colombia could teach Donald Trump a thing or two about building a beautiful wall. The Spanish colonists constructed one in Cartagena. After half a millennium, it stills stands, 8 miles of thick stone. It remains a beautiful thing, perhaps the most beautiful object in what is effectively the western hemisphere’s oldest and most beautiful city.

At least in this case, a beautiful wall is grand thing to behold. But, memo to Trump: the wall did not make the city safe or do the Spaniards much good. Only 25 years after the wall was completed, the Spaniards were ousted entirely from South America.

Today, Las Murallas are the ancient city’s prime attraction. There are actually two, an inner and an outer wall, which took two centuries to build. But the walls are more than a tourist attraction.

They are also the dividing line between the polished and touristic byways of the old city and the modern metropolis where a million real Colombians lead their daily lives amid multilane highways, towering office blocks and skyscraper apartments lining seaside beaches.

High-profile tourist attractions are always a kind of fantasy world. Add the 1 million visitors, most pouring out of cruise ships, and the thousands of police and soldiers assuring their safety in an insecure land, and the fantasy can quickly wear thin, as it did for me.

After flying from the United States to Cartagena and arriving late at night, we spent a couple of happy days getting to know what was, for my wife and I, a new country. We explored the old churches and palaces, the alleys and plazas and shops of the historic district, walked along the ancient walls and visited the largest fortress Spain ever built in its colonies.

We also spent a few hours swimming in a clean, calm sea at a fine but unheralded and un-touristed beach at the end of the bus line south of downtown. Our “Lonely Planet” guidebook insisted wrongly that the only good beaches were on touristic offshore islands, but the sister of our hostess at the house where we stayed in Cartagena wisely sent us off to her own favorite beach, which at the time was nearly deserted.

We passed our nights across a bridge from the old town, in Barrio Manga, a pleasant modern neighborhood of shops and apartments, where the Colombian middle class goes about its daily business. Seeing these two juxtaposed sides of Colombia—the artificial world of the colonial town and the real world of the modern city—was an instructive introduction to a complex country where reality is never one sided.

Later we repeated the schizoid experience, during two visits to separate districts of the vast capital, Bogotá, with a population of 8 million. Again, we witnessed the contrast between two juxtaposed but sharply contrasting worlds. But that was a month later, at the end of our trip, our final experience with how Colombians navigate their severed society.

There are lessons here: real places are more interesting than shiny replicas, and reality has a stubborn way of surviving even the most massive tourist onslaught—you just have to have the luck and the persistence to hunt it down.

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Impregnable but useless: Colombian tourists in Cartagena take snapshots of Castillo de San Felipe de Barajas, Spain’s largest colonial fortress. Photo by Thelma Bowles.

Leaving Cartagena after three nights, we headed west along the coast on a long bus ride (actually a taxi ride and two bus rides, typical of Colombian transportation) to the village of El Zaino, near the entrance to Colombia’s most famous and most heavily used national park, Tayrona.

The house where we stayed was a wonderful little place hanging over the banks of a small river, the Rio Piedra, with cool bathing pools in which we happily splashed and a hanging bridge over which we precariously tottered.

The friendly matriarch of our family hostel told us, “My husband was killed. My son is dead.” It was our first direct encounter with the terror that has decimated Colombia’s rural population over the past 50 years. Violence is winding down now, but many Colombians have been so badly scarred that the past is the last thing they want to talk about. We didn’t question our hostess about the details of her family tragedies, and she didn’t volunteer any.

The morning after our arrival in El Zaino, we got an early start and hiked a 14-mile circular route in the lovely park, through the jungle, along cliffs and past beaches ranging from the wild and perilous to the tranquil and safe. We even heard of a nude beach but turned back before reaching it.

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Early the next morning we left the Caribbean coast for the interior, the real Colombia. A long day of bus rides took us to Mompox, one of the most remote villages in Colombia, if also one of the most storied.

Mompox is on an island in the Rio Magdalena. This is not just another river. Aside from the Andes, it is the country’s most important geographical feature, the Mississippi River of Colombia. Nearly 1,000 miles long, it is the historic, cultural and economic link between two very different worlds—the hot, humid, crowded and touristy Caribbean coast and the high, cool, fertile mountains with glaciers, active volcanos and three cities each with more than 2 million people.

The Magdalena Valley was the home of Latin America’s most important writer, Nobel Prize-winner Gabriel Garcia Márquez, as well as the setting for his stories of suffering and endurance at the hands of an erratic and often merciless fate.

Spaniards used the river to access the interior from the coast. For them and subsequent Colombians, the river was the major trade route, and Mompox was one of the most important commercial hubs in the valley.

But time treated the river and its inhabitants harshly. The river became so heavily silted that most navigation was impossible. It became so polluted that Michael Jacobs, in his 2012 nonfiction adventure story, “The Robber of Dreams,” recounts that seamen who accidentally fell overboard in a collision died of poisoning from the river water. He wrote that getting to the island was so torturous, requiring a jeep trip on a muddy track and a 20-minute canoe ride, that few attempted it.

Today, a new bridge and paved road have made the island more accessible, but it is still far off the beaten track—for us, a happy circumstance, for it gave us the chance to explore a town and a region that seem little changed from the 19th century.

We strolled along the banks of the famed river. We took a three-hour boat trip on the wide river and its narrow tributaries, during which we encountered more bird species than I have seen in New Mexico in 30 years. We spotted eagles and kingfishers, fought off a fish who jumped right into our boat and paused inches away from giant iguanas. Monkeys and caimans hang out in the jungle surrounding a large lagoon.

The captain offered us a chance to jump over the side and splash around in the shallow lagoon, but mindful of Jacobs’s description of the poisons in the river, we refrained. Several teenage Colombian tourists, however, had no such qualms. (Everywhere we went in the country, except Cartagena, Colombian tourists far outnumbered foreigners.)

Mompox itself seems frozen in time, with its narrow streets and whitewashed buildings and old churches. Jacobs described it 20 years ago as a place that “did not seem at first like a place of bricks, mortar and stone, but rather some memory uncovered from my distant past.”

Marquez wrote, “Mompox does not exist. Sometimes we dream about her, but she does not exist.” However, it does.

The little town of a few thousand residents was once one of the great commercial hubs of the Spanish world, with the oldest university in the Caribbean area and a French-donated Statue of Liberty older than the one in New York. A battalion of Mompox volunteers formed the ablest fighters in Simón Bolívar’s army that defeated Spain in the early 19th century.

Now, with a typically Colombian mixture of fear and hope, the town in the middle of nowhere is imagining the tourist mobs who might some day invade across the new bridge.