There is a town in Turkey where the entire population lives in underground cave cities.
Why it is true
Derinkuyu and other underground cities in Cappadocia were carved into soft volcanic rock, with multiple levels including stables, churches, and wells, serving as a refuge against invasions.
Source: Architecture
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This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.