If you were an early Christian fleeing Roman persecution, Turkey offered more than 200 underground cities, 40 of which contain three levels or more. The largest found so far, in Derinkuyu, has eight floors and extends to a depth of 85 meters, covering as much as 7,000 square feet (some floors haven’t yet been excavated).

It wasn’t a bad life: The larger complexes had rooms for food storage, kitchens, churches, stables, wine and oil presses, and shafts for ventilation. At its height, the city at Derinkuyu could accommodate 50,000 people.