5. City of the Dead, Cairo
City of the Dead in 1904. Image in Public Domain by Eduard Spelterini
The City of the Dead on the border of Cairo, Egypt, was built as a cemetery starting in 642 A.D., but is now also home to anywhere between 50,000 to a million people that are still living. Economic factors have contributed to the increase in population, particularly after the Egyptian Revolution in 2011. Functionally, it’s just like any other suburb with power lines and a post office but conveniently the upkeep of the mausoleums provide both income and housing.
Image via Wikimedia Commons by Bertramz