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Teotihuacan, Mexico
This is probably one of the most enigmatic man made wonder in the world since it was built a long time ago and original builders are unknown till today. The city was designed to be a large urban complex stretching over 20 square kilometres with many distinctive pyramids and when it was habited; it could have housed over a hundred thousand people. The city was abandoned about 1,400 years ago and taken over by the Aztecs much later and redeveloped into an urban centre. The current name was given by the Aztecs.