Derinkuyu ('Deep Well') is an amazing underground city discovered about 50 years ago in Turkey. Some of the theories of why it was built include early Christians hiding from the Romans, a culture from 12000(Gobekli Tepe?) years ago going underground because of an atmosphere (impact) problem, a culture hiding from ancient aliens and someone escaping what the earliest text describe as the 'evil winters' of prehistory. www.ancient-wisdom.co.uk/turkeyderinkuyu.htm