#3 Area 51, Nevada, US
Hidden in the middle of the barren Nevada desert, Area 51 is a secret American military base whose purpose has always been unknown to the public. What goes on inside the base has led to decades of wild speculations, including the famous alien conspiracies. However, it likely serves as a site for development and testing of experimental aircrafts and weapons. One thing is for sure though – whatever happens in Area 51 is not meant to be seen by the public as the access is strictly forbidden.