At the end of more than 1,200 mountainside steps in the near-impenetrable tropical forest of Colombia’s Sierra Nevada lie the ruins of an ancient, abandoned city. Uncovered in the 1970s, the incredible city was one of the important archaeological discoveries of the 20th century, revealed to the world as Ciudad Perdida, or the “Lost City.”

Perhaps most remarkable about Ciudad Perdida is the fact that it was built some 650 years before Machu Picchu, around 800 CE. The city was also massive by ancient standards—believed to be home to some 2,000 to 8,000 inhabitants—and an impressive feat of engineering, built along a steep mountain ridge nearly a mile above sea level. A complex network of stone bridges and drainage systems has maintained the city throughout the test of time.

The site is believed to have been the seat of power of the Tairona kingdom, which spanned throughout the Sierra Nevada and the northern region of Colombia. It was likely abandoned in the 16th century amid the arrival of Spanish conquistadores.

Yet despite its name, the “Lost City” was never really lost, at least not to the descendants of the Tairona people that still occupy the region, today known as the Wiwa, Kogi, Arhuaco and Kankuamo. Though their ancestors abandoned the city centuries ago, the indigenous people of the Sierra Nevada de Santa Marta never forgot about it. When the site was “discovered” in the ’70s, indigenous leaders quietly asserted that they knew of the city’s existence all along. In fact, they had never stopped visiting the site, known to them as Teyuna, over the centuries. They simply had always been careful to keep its location a secret from outsiders in order to avoid precisely what happened after the looters found the city.

Closed off for years, the site is now open to visitors—though only the most dedicated (and physically capable) of adventurers can visit the Lost City, which to this day is only accessible by a 27-mile hike through treacherous terrain and an inhospitable climate.