Exploring the Fascinating Underground City of Derinkuyu in Turkey's Cappadocia Region. #mystery

Derinkuyu is a large underground city located in Turkey's Cappadocia region.
Built by Phrygians beginning in the 8th-7th centuries BCE and expanded by early Christians, it sheltered up to 20,000 people below ground.
The ancient city extends 85 meters deep across 18 levels, though only half is accessible today.
It contains homes, stables, churches and storage areas hollowed out of soft volcanic rock.
Ventilation shafts, wells and large rolling stone doors enhanced liveability underground.
1. When was Derinkuyu likely first built?

2. How many levels does it extend down and how deep is it?

3. What types of structures did it contain to shelter and support life underground?

4. What ingenious engineering features helped provide air flow and access underground?