Göreme

Apparently the name of the town meant "cannot be seen" in Turkish (gör root for "to see" + negative suffix -eme.) Because although the fairy chimneys were very much visible, it was very difficult for jaded military patrols who didn't know better to spot signs of human habitation amidst this surreal but entirely natural volcanic moonscape.

It was pretty cool. There was even a jandarma (police) station inside a fairy chimney. The only downside was that ventilation was always not very optimal. It was invariably comfortably cool inside, but a little stuffy with a few hints of mould. They should have worked on ventilation technology.
But then again, maybe they did have the technological know-how, but just didn't implement it in the fairy chimneys for some reasons. The underground cities---or at least Derinkuyu, which we visited---had very fresh air even seven storeys below ground, courtesy of an elaborate system of ventilation shafts and tunnels. These underground cities were truly invisible too: were it not for the concrete shell of an entrance built for the benefit of tourists, we would have been entirely clueless to the presence of the vast twelve-storey complex of tunnels we were standing above.

Can you imagine staying for weeks, months even, cooped up deep underground, or holed up in the mountains, cut off from the rest of the world and for all intents and purposes invisible to them? Life back then cannot have been fun.