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A door stands open at an entrance to the Vivos Shelter and Resort during a tour of the facility in Atchison, Kan., Tuesday, June 18, 2013. (AP Photo/Orlin Wagner)

Kansas underground shelter

Robert Vicino is creating what he calls the world's largest

private underground survivor shelter --  the Vivos Survival Shelter and Resort -- using a complex of limestone caves

dug more than 100 years ago beneath gently rolling hills overlooking

the Missouri River. (AP)