Conversation

I just learned that in 1963, some guy in Turkey was renovating his house when he found a hidden room behind a wall. He started exploring and discovered what would turn out to be a complete underground city, 85 meters deep and big enough to hold 20,000 people. This is the underground city of Derinkuyu, built some 1000 years ago by the local population to hide from invaders.

https://en.wikipedia.org/wiki/Derinkuyu_underground_city

Thanks to the It's Probably (Not) Aliens podcast for this: https://probsnotaliens.com/