It has a long heritage. In fact, Cappadocia in Turkey is thought to have housed 20,000 people in one big underground network! https://www.bbc.com/travel/artic

It has a long heritage. In fact, Cappadocia in Turkey is thought to have housed 20,000 people in one big underground network! https://www.bbc.com/travel/article/20220810-derinkuyu-turkeys-underground-city-of-20000-people https://www.bbc.com/travel/article/20220810-derinkuyu-turkey...