Derinkuyu, Turkey: This ancient underground city in Cappadocia extends to a depth of about 60 meters (200 feet) and could once shelter thousands of people.
Montreal’s RESO, Canada: Known as the "Underground City," this extensive network of interconnected buildings, shopping centers, and hotels spans 33 kilometers (20 miles) beneath Montreal, allowing residents to travel year-round without going outside.
Coober Pedy, Australia: This opal-mining town in South Australia is famous for its dugouts—homes and businesses built underground to escape the extreme heat of the outback.
Wieliczka Salt Mine, Poland: This historic salt mine near Krakow has been in operation since the 13th century. It features underground chapels, tunnels, and even a museum, all carved from salt.
Baku’s Underground City, Azerbaijan: Known as Baku’s "Underground City," this network of ancient tunnels and caves once served as a refuge for residents during invasions and attacks.
Capadocia, Turkey: Not just limited to Derinkuyu, the region of Cappadocia has numerous other underground cities, including Kaymaklı and Özkonak, featuring intricate systems of tunnels and rooms used by early Christians for protection.
Beijing Underground City, China: This vast network of tunnels and bunkers was built during the Cold War to protect citizens and officials. It includes residential areas, hospitals, and shops designed to sustain life underground.