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We often think of abandoned cities in the form of "ghost towns" typically found in the western United States. Whole towns left empty after the gold rush of the mid-19th century. However, there are entire "modern" cities that have been left completely abandoned all over the World.
Some photos from the cities, when you follow the link, include: Kowloon Walled City (a city just outside Hong Kong, China), Gary, Indiana (some 30-minutes from Chicago), Ruby, Arizona, Wittenoom, Australia and others.
There are some glaring omissions, like Chernobyl for example, but I don't think this was supposed to be a complete list. It is interesting to see the many reasons why whole cities and towns could be left completely abandoned and left standing, as if people just packed up, left for vacation, and never returned.