Far below the noisy bars and busy streets of Cadiz in southern Spain, speleologist Eugenio Belgrano shone his flashlight on a silent, empty world. The beam shot through a pitch-black tunnel and hit a rock wall, where people from bygone eras had scrawled their names along with the year they’d been there: most were dated between 1600 and 1700.  

“It’s you in the darkness, in a place where the last humans were centuries ago,” Belgrano said. “And it’s in the same condition as it was then.”

Belgrano, 29, was 11 years old when he and his friends found a portal to this subterranean realm. Forgotten for decades in a city known for its beaches and sunshine, the network of tunnels had  became an urban legend, one that enticed the children to climb down a city sewer to search for them. There they found an 823m-long tunnel that led to a small forest above ground, part of an ancient labyrinth of passages, caves and burial sites that cover an estimated 60km under the city.

Parts of the winding network date as far back as 3,000 years, when the Phoenicians founded the port city. The Romans expanded the tunnels, and more were added between the 16th and 18th centuries. Soldiers, smugglers and secret society members are among those who have passed through these narrow, musty corridors.

In the Roman era in Cadiz, which began in 200 BC and lasted 700 years, the tunnels were used to move water through the city and store hypogaeum, or underground tombs. Jews and members of the Masonic Rosicrucian Order later fled to the tunnels to escape persecution or perform rituals during the Spanish Inquisition from 1478 to 1834. After English and Dutch troops captured Cadiz in 1596 during the Anglo-Spanish War, the city added more tunnels and built a defensive wall to hide military troops and block enemies from digging their own clandestine entries into the city.

“It’s a time machine,” Belgrano said. “You go down 5m and you are 400 or 500 years behind. You don’t realize you live in the 21st Century. When you are down there, you disconnect from the world. You’re [on] another planet. It transports you.” 

Dedicated to exploring as much of the network as he can, Belgrano lowers himself down by rope everyday, carefully watching the domed ceilings for signs of collapse and holding a gas detector to check for toxic carbon monoxide and combustible methane. He wears non-flammable clothing, a breathing mask hooked to an oxygen tank, a helmet in case of loose rocks overhead, and a headlight to see through the darkness. It’s always uncertain what lies ahead.

Deep below, Belgrano can sometimes hear the voices of people above him. He may step on rocks, encounter human bones, find snakes and rats, or wade into brown, neck-high water. Due to the stifling humidity, the air always feels warm, despite the average year-round underground temperature of 20C. He and his small team of excavators, part of the Association of Investigators of the Cadiz Underground, which he founded, are constantly exploring, taking pictures and documenting what they see, sometimes into the early morning hours.

He’s found signed architectural drawings on the walls made by 17th- and 18th-century engineers studying the construction of the sturdy underground structures. He’s even unearthed a document from the early 1800s describing the voices of ghosts beneath Cadiz – who were actually smugglers carrying contraband through the tunnels.

Since his initial find 18 years ago, Belgrano and his team have discovered many more portals throughout the city – but most are on private land and are often blocked up with dirt and water.

“Everyone that has a hole on their property wants to know why it’s there, but nobody is brave enough to go in,” Belgrano said. “So they call us to tell them what is under their house.”

During one of his expeditions underneath a residential building, Belgrano discovered a catacomb built in 1633 that he opened to the public last year, a venture he funded himself. Catacumbas del Beaterio (Catacombs of the Sanctorum) was the burial place for nuns from a 17th-century Franciscan Order. It may have also been a meeting place for members of the mystical Masonic Rosicrucian Order, as their rose-and-cross symbol was found etched on a wall. Centuries later, when General Francisco Franco’s troops took over Cadiz during the Spanish Civil War, residents of the building above hid here. It’s an intimate space that can fit no more than about 20 people at a time.

Belgrano also uncovered the pozo de la Jara or Rockrose, which was the only source of potable water in Cadiz until 1666. Christopher Columbus purportedly loaded his ship with water from the well before his second trip to America. The well was sealed and lost for more than 300 years, until Belgrano found it under the bedroom of a house.

But despite all these years of exploring, he’s only seen a small portion of the maze beneath the city. He is working to restore more tunnels and open them to the public, with the next one scheduled to open in December, housing an underground exhibition of photos and videos of all the tunnels and caves he’s explored so far. In the meantime, only Belgrano and his team have access to the underground realm.

“When we find an entrance, we keep it a secret,” he said, adding, “There isn’t a book that tells you how to find or enter an underground cave. It’s a process we’re creating now.”

He remembers his first trip into the underground tunnels, 18 years ago.

“It was dangerous,” he said. “We didn’t know where we were going.”

Belgrano hopes to guide others through more of the long-unexplored world – and protect it for future generations.

“The tunnels aren’t given the importance they deserve. They have been there for centuries, and with the construction of buildings and parking lots, we are destroying that underworld,” he said.

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