Something a bit different: Derinkuyu in Cappadocia, Turkey.

It is believed that the underground cities of Cappadocia were initially built during the eighth and seventh centuries BCE by the Phrygians, who carved their living spaces into the region’s soft volcanic rock. There are around 200 cities in total in Cappadocia, with the most visited including Derinkuyu and Kaymakli.

The idea behind the subterranean cities was to protect the inhabitants from foreign invasion, allowing thousands of people to live their lives in total secrecy. During the 14th century, the caves provided Christians with a safe haven from the threat of the Mongolians during the assaults on Timur. Even during the 20th century, they enabled people to save themselves from persecution during the Ottoman Empire.