One recent glorious Sunday morning in Barcelona, my friend Elies and I are walking down the Rambla to meet our tour guide in front of the ornate 19th-century Liceu opera house. It's 11:30 a.m., and tourists are swarming the historic promenade, sitting down for an early lunch, armed with selfie sticks and maps to study.

We dodge a swarm of cruise-ship passengers, who trail behind a Pied Piper-like guide carrying a little flag, and then we spot Jaume Rodriguez Vogt, a tall, friendly-looking man of about 50. He's dressed in a red T-shirt, baggy jeans and yellow flip-flops, holding a folder with "Hidden City Tours" printed on it.

I thought Jaume might start the tour with some information about the history of the opera house or its architecture, but he leads us instead to the entrance of a nearby bank. Flies are swarming. It smells faintly of urine. We spend a few minutes making introductions and engaging in small talk until Elies finally asks, "Sorry, but why are we standing here?"

"Ah," Jaume says, turning to face the ATMs in the bank's anteroom. "During the crisis, the banks were tolerant. As long as you left things clean and didn't leave wine bottles around, they let people sleep here during the winter."

This is our first hint that this won't be any ordinary city tour. As the name suggests, Hidden City shows visitors a side of Barcelona that most would prefer to ignore, by offering a glimpse into how the city's 3,000 homeless residents experience daily life in one of the world's most visited tourist destinations. It isn't a pretty picture, but the experience highlights our shared humanity in a way your average bus tour could never hope to match.

When former market research consultant Lisa Grace found herself out of work in 2012, she went looking for a change. She launched Hidden City Tours in Barcelona two years later, after reading an article about a similar endeavor in London.

"It was literally my lightbulb moment of, 'Ding! This idea could work in Barcelona, with large numbers of tourists and business travelers and a huge homeless problem,' " she says. "I thought about putting one to work to solve the other."

With its 80-hour training program, Hidden City employs as tour guides a handful of people, like Jaume, who have experienced homelessness in the city. One is a freelance architect who found himself sleeping in an ATM shelter after a layoff; while another guide worked as a chef (he now draws upon that experience as a chef when giving tours of the famous Boqueria market).

Hidden City attracts socially conscious travelers, and Grace says that the guides' personal stories strike a chord with visitors.

"For many, it's the first time they have come face to face with a homeless person," Grace says. "People are often shocked at how our guides ended up on the streets, [realizing] that life is cruel and society has failed these people, rather than the other way 'round."

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"I don't like the word 'homeless'," Jaume says as he guides us off the Rambla and into the medieval streets of the Raval. The son of a German nurse and a Spanish doctor, Jaume worked as a policeman, a TV producer and a taxi driver until back problems prevented him from spending long hours behind the wheel. He resorted to picking up trash, but when the global financial crisis hit, that job wasn't bringing in enough to pay the rent. Before he was evicted, he left his apartment and started sleeping among the marble statues and gold-plated fountains in Ciutadella Park.

"I was scared I'd become one of those smelly addicts with a beard and dirty clothes," he says. "I realized almost anyone can get into this situation."

The economic crisis took a massive toll on Spain, where unemployment reached an unprecedented 27 percent in 2013 and some 350,000 people have been forced from their homes. Complicating matters, about half of those who have become homeless in Barcelona suffered from a mental illness, according to a 2010 study.

Jaume slept in the park for three months before a city social-services worker brought him to a shelter; soon after, he met Grace and started training to become a guide. He says the experience changed his ideas about what homelessness looked like. One of his Hidden City co-workers has a university education, for example, and most speak several languages. Jaume speaks English, Spanish, Catalan and German fluently.

He takes us past the Maritime Museum, which draws visitors with its reproductions of 16th-century galleons. But to those who have experienced homelessness, it is perhaps better known for its proximity to a controversial social service called a narcosala, or "drug room," where addicts can get high in a secure space that is monitored by doctors.

"It's important they don't use in the street," Jaume says.

Right then, a city worker appears, holding a biohazard bin and a trash-grabber, scanning the ground for stray needles. "We find far fewer now than before," he says.

"The day is really long when you're living on the street, even if you're not an addict," Jaume says as he leads us up a narrow street, past a grassy area where a group of men sits surrounded by shopping carts. Younger men use the carts to scrape together a meager living collecting scrap metal. But walking 15 to 20 miles a day while pushing a cart wasn't an option for Jaume, who was in his late 40s when he found himself sleeping in the park.

"What did I do? Something much easier," he says. "I made soap bubbles."

Longing for an activity to fill his days, Jaume met a Czech couple who taught him to entertain kids in the park for tips. On a good day, he earned about 20 euros.

"Doing the bubbles occupies the mind; you get to interact with children," he says. "When you're homeless, having a little money is psychologically important. When you don't even have a dime, depression grows."

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The tour continues along the lively Rambla del Raval, where sidewalk tables are packed with diners feasting on kale salads, while down a side street Jaume points out a pair of inconspicuous organizations that provide hot meals, free showers and clean clothes daily.

"There are a lot of people who are homeless and you wouldn't even know it," Jaume says.

Just when the tour seems like it might be a thinly veiled public service announcement for Barcelona's social-services agencies, Jaume pipes up with some fun, practical tips, too. He recommends that we come back in the evening for a drink at Bar Marsella, one of the city's oldest watering holes, and points out an under-the-radar flamenco bar where top dancers perform on Saturday nights and the cover charge is only four euros.

Nearing the end of the two-hour tour, we stroll down the Carrer de l'Hospital and into the courtyard of a stunning medieval hospital that now houses the National Library of Catalonia. Jaume says the area is a popular meeting point for the homeless, in part because the library leaves out free newspapers for anyone to read. We walk past a young couple lying on a mattress on the ground, their eyes half-open and glassy, and two guys passing around a bottle of cheap wine.

Next door is a refuge for homeless cats, owned by an eccentric woman from the neighborhood. Peering through the bars of a fenced-off garden, we can see about two dozen calicoes and tabbies lounging in their beds, taking shelter from the midday sun. Jaume says that most of them are not feral but rather house cats that were abandoned, ill-equipped for life on the streets. Kind of like him.

He waves at them through the bars and smiles. "It's just a nice place for them to eat, sleep and be together," he says.

Between Hidden City and his gig as a hotel shuttle driver, Jaume now earns enough money to pay rent on an apartment that he shares with two friends. His father, a doctor who lives in Barcelona, still doesn't know about his stint on the streets.

"If you told me in 2003 that I'd be homeless, I'd say, 'Dream on,'" Jaume says. "Never say never."

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Kroth is a journalist based in Mexico City. She can be found on Twitter at @theemaya.