By Alex Rodway, CNN

(CNN) — Six tourists wearing hard hats and heavy overalls sit, cramped up in a narrow mineshaft, with barely enough space to kneel. The local tour guide pulls out a disposable lighter, ignites a bright green fuse with it, and calmly ushers everyone backward. “Any moment,” he says.

A moment later, a powerful shockwave rips through the tunnel, tailed by a dust cloud.

He’s just set off a stick of dynamite bought at the local market earlier that day by one of the tourists — it cost 13 Bolivianos (just under $2). The Bolivian mining city of Potosí is the only place in the world where members of the public can legally buy dynamite.

“For the miners, the most essential thing is dynamite,” says Jhonny Condori, a Potosí mine tour guide. “If you don’t know how to handle it, it’s dangerous.”

But for experienced miners, it greatly speeds up the rate at which they can extract minerals.

Centuries old, Potosí’s network of mines is extensive. Miners run up and down long, narrow passageways, pushing carts full of fragmented rock along worn railway tracks — it’s a scene reminiscent of something from “Indiana Jones and the Temple of Doom” or Wario’s Gold Mine in Mario Kart.

Potosí is over 4,000 meters (13,000 feet) above sea level, making it one of the highest cities in the world. Its narrow streets and the red-tiled roofs and stucco walls of its buildings hint at its Spanish colonial past.

Much of the mining takes place within the adjacent, red-colored “Cerro Rico” (literally “Rich Mountain” in English) — so named because of the vast wealth it once brought to the city. Today, “Potosí is considered one of the poorest regions in all of Bolivia,” says Julio Vera Ayarachi, another local tour guide.

The Cerro Rico’s silver lining

Legend tells that the rich silver deposits of the Cerro Rico were first discovered by Diego Gualpa, an indigenous Andean prospector, who stumbled across them in 1545. “The secret got out. You can’t hide that kind of news,” says Kris Lane, professor of liberal arts at Tulane University in New Orleans, and author of “Potosí: The Silver City That Changed the World.”

Before long, Spanish colonizers — who had arrived in the region just a few years before — caught wind of the discovery and began exploiting the mountain’s abundant silver.

“It developed very quickly into a kind of nightmarish place,” says Lane. “It’s a place that’s lawless, it’s a place of forced labor.”

Indigenous people were obligated to work for and produce material tributes to the Spanish king, under a system that was “very close to enslavement,” he adds.

A surge of wealthy merchants began arriving from around the world to build infrastructure and profit from the mines. As techniques improved, conditions declined further, says Lane. Toxic mercury was introduced to the refining process, for example, which leached into the environment and led to the deaths of many. The Cerro Rico became known as “The Mountain That Eats Men” — a name that persists among miners to this day.

Potosí soon grew into to fourth largest city in the Christian world, with a population of more than 200,000 by the end of the 16th century. It’s thought to have supplied 60% of the world’s silver at the time, funding the Spanish empire and other dynasties around the globe.

“Silver crosses borders in a way that a bronze coin or a copper coin could not,” says Lane. Its relative scarcity gave it intrinsic value and “people came to expect that Potosí silver was trustworthy,” he says.

However, over time, the once seemingly endless silver reserves began to dry up. By the time Bolivia declared its independence in 1825, almost all the silver had already been mined and Potosí became a shell of its former self.

Though mining still goes on in there today, much of it is for cheaper minerals like tin and zinc. Hundreds of miles of mine shafts have made the mountain unstable — as a result, it is currently the “most dangerous time that the mines have witnessed,” says Lane.

Worshipping the devil

Nevertheless, “in terms of mining, well, not much has changed,” says Oscar Torrez Villapuma, another local tour guide. Miners in Potosí still pray to the same gods, follow the same rituals and die of the same respiratory diseases as their ancestors, centuries before, he continues.

Each mine shaft entrance in Potosí is marked by a horned, devil-like effigy — known locally as “El Tío” (the uncle). El Tío is usually red, decorated with colorful ribbons around his neck, and frequently portrayed with a large, erect penis: a symbol of fertility.

“We are very polytheistic, we believe in various gods,” says Condori. While many indigenous Andeans worship the Christian God introduced by their Spanish colonizers, most also revere the Pachamama — or Mother Earth — a feminine, Incan divinity.

Naturally, “there must be some underworld male figure that protects Pacha Mama from over-exploitation,” says Lane, providing one possible origin for El Tío. Villapuma suggests, instead, that the figure was introduced by colonial bosses to intimidate their indigenous workforce, “but nowadays, he is the one who gives us fortune,” he says.

Either way, El Tío statues today are littered with coca leaves, cigarette butts, empty beer cans and spirit bottles: offerings from miners and tourists, so that he might grant safe passage through the mine and reward them with abundant minerals. Locals also regularly slaughter llamas and smear the animals’ blood at mine entrances in the hope of quenching El Tío’s thirst for blood.

The everyday

Life expectancy for Bolivian miners is thought to be as low as 40 years.

Common early deaths result from frequent accidents in the mines and silicosis, a chronic lung disease caused by breathing in silica — “essentially ground glass is what it amounts to,” says Lane.

“It was a sign of toughness that you didn’t wear a mask,” he continues, explaining how this exacerbates the issue — “and mine workers in Bolivia are seen as the toughest nuts to crack.”

The legal minimum working age in Bolivia is 14 years old, but loopholes mean that children can often work from much younger. Some reports have suggested that children as young as six still work in Bolivian mines.

“In this space of apparent horror, you find comradery, creativity… music comes out of this place, interesting poetry, lots of cultural fluorescence,” says Lane.

Potosí hosts a vibrant “mining carnival” between February and March each year, which draws in huge numbers of travelers. Tradition dictates that miners dress in their work clothes and dance through the town, drinking beer and wielding El Tío puppets. Local women — known as Cholitas — wear elaborate dresses and perform choreographed displays to the music of marching bands.

Following the festivities, many of the tourists return to Bolivia’s capital, La Paz, along the same bumpy overnight bus route that brought them to Potosí. Miners and their families, however, remain, returning to their often brutal, repetitive daily routines for another year.

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