Though it may be the most famous, Nevada's Area 51 isn't the only top secret location in the world.
Come with us on a guide through the world's most top secret nuclear bunkers, defence bases and weapons testing ranges.
What: Yongbyon Nuclear Scientific Research Centre
Where: North Korea
Built in 1979 it wasn’t until 1985 that North Korea even declared the existence of this 5 megawatt nuclear reactor.
Since that time UN inspectors have been denied access and claims that it has been closed have circulated, only for it to appear on radars earlier this year when a test rocket was launched from the site.
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