Coober Pedy is small town in South Australia which is famous by precious opals that are mined in its nearby but also it is famous by pretty weird underground residences. Those structures are called dugouts by the local residents and primarily they were built with a purpose to escape from daytime heat which is unbearable down there in Australia.
The name they use for those structures might sound too simple for the complex of buildings which is really existing there. They even have a church built there underground. If you come around there in summer, you might want to stay in underground motel.