>>10071062>there is no evidence on ancient DUMBs>The Derinkuyu underground city is an ancient multi-level underground city in the Derinkuyu district in Nevşehir Province, Turkey, extending to a depth of approximately 60 metres (200 ft). 20,000 people were living in this city underground in 800 BC. Did they construct it or did they simply find it and move in? Also it’s not fully discovered so they don’t know how deep it goes.
https://en.m.wikipedia.org/wiki/Derinkuyu_underground_city 