Carved from the soft volcanic rock of Cappadocia, Turkey, the subterranean UNESCO World Heritage site of Derinkuyu could shelter up to 20,000 people. What unique engineering feature did its residents use to seal off individual tunnels and protect themselves from invaders?

Wonders carved from stone
Nature's strangest sanctuaries
Lost empires and jungle ruins
Masterpieces of human ingenuity
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Master of The world's wildest heritage sites
schopenhauer Kailasa Temple
Carved from the top down, a mountain of stone! (A mountain of stone!) / Kailasa stands on its own! (Stands on its own!)

schopenhauer An ancient desert metropolis carved directly into sandstone cliffs by the Nabataeans over two thousand years ago.

schopenhauer Cappadocia's massive subterranean city could shelter up to 20,000 people from invaders deep beneath the earth.

schopenhauer Match these unique stone monuments to discover the secrets of UNESCO World Heritage sites.
Lalibela's tunnels: Lalibela's churches are connected by a maze of dark, narrow underground tunnels designed to symbolize the journey to heaven.
A large single block of stone shaped into a monument or architectural structure. At Lalibela, thirteenth-century builders crafted eleven spectacular churches, each carved as a single subterranean monolith.
Carved deep into soft volcanic stone, the ancient subterranean city of Derinkuyu in Turkey is an engineering marvel. How was this massive underground site accidentally rediscovered in 1963?
The monolithic rock churches of Lalibela in Ethiopia, a UNESCO World Heritage Site, are famous for which unique architectural feat?
Which ancient civilization carved the desert city of Petra in modern-day Jordan?
In what year were the ancient Buddhist Ajanta Caves in India rediscovered by a British officer?
Which Ethiopian king ordered the construction of the eleven monolithic stone churches in Lalibela?
What was used to seal the tunnels of the Derinkuyu underground city from intruders?
Along which river's horseshoe-shaped gorge are the Ajanta Caves in India located?
