Derinkuyu

Derinkuyu is an underground city in the Cappadocia region of central Turkey, 40 km from where I was staying in Göreme. It was first excavated in the 7th or 8th century BC, then extended in the Byzantine era. When invading armies came through, it was a place for the locals to hide until the danger had passed. 

The first thing to note is that it is extremely difficult to photograph an underground city. Think petrified snow fort; it's cool to experience, but you can only do that from the inside. So here's a map to give an idea of the layout of this place (hint: random.)

Wells running through but not to the surface in some cases so the inhabitants couldn't be poisoned. Religious school on one of the upper levels. Cruciform church on the lowest level.

Door plugs that look like mill stones so each level could be sealed off. There are little chambers off the staircases where the plugs recede, but it's still unclear to me how they were moved. 

Long table built into the floor.