The world's largest underground city housed more than 20,000 people.

World History

B uilding an 18-level underground city may sound like the project of an advanced future society, but the world's largest underground metropolis was actually constructed around 1200 BCE. The ancient subterranean city of Elengubu, now called Derinkuyu, lies in the semi-arid region of Cappadocia in modern-day Turkey. Tourists can meander tunnels and walk among subterranean rooms, stables, schools, wineries, and even a chapel — all underground. At its peak, during Islamic raids on the Byzantine Empire in the seventh century, Derinkuyu housed up to 20,000 people.

While the origin of the site remains a mystery, experts theorize that the Hittites, a superpower of the Bronze Age, likely built the first few levels while under attack from the Phrygians, who expanded the project when they moved into Central Anatolia after the Hittites' collapse. Although the Phrygians were skilled architects, the surrounding landscape also aided in this ambitious construction effort. Due to the area's semi-arid nature, Cappadocia's soil is easily malleable and its rock easily moldable. Three volcanoes — Mount Erciyes, Mount Hasan, and Mount Melendiz — formed the region millions of years ago, and the pyroclastic material found in the area could be carved with simple tools and little effort. Today, for 60 Turkish lira (about $2), visitors can once again descend into this subterranean world and experience life underground.

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By the Numbers

Distance (in feet) of the world's deepest human-dug hole

40,229

Running time (in minutes) of Indiana Jones and the Last Crusade, featuring the underground city of Petra

127

Did you know?

The world's largest cave was discovered by accident.

The world's largest cave is Hang Sơn Đoòng ("Mountain River Cave"), located in Vietnam's Phong Nha-Ke Bang National Park. Encompassing an incredible 1.35 billion cubic feet, this cave is so big that it contains its own weather system (clouds included), especially during Vietnam's warm and muggy spring months, when moisture forms at the cave's mouth. Despite its immense size, Hang Sơn Đoòng was not discovered until 1990, and only then by accident. A local named Ho Khanh was exploring the jungle for timber and food when he unexpectedly spotted the gaping maw of a limestone cliff with clouds billowing out of it. As the site seemed too perilous to explore, Khanh moved on and promptly forgot its location. It wasn't until a later conversation with two members of a British cave expedition that Khanh realized what he'd discovered. It took him almost two decades to relocate the cave, but in 2009, he led a team of experts and surveyors to the site of his discovery.

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