A huge doomsday bunker complex the size of a city could save 10,000 people from a nuclear war, a deadly virus or an asteroid strike, its makers claim.
Hundreds of concrete military bunkers in South Dakota, US, are being transformed into a survival shelter in case of the apocalypse.
Vivos, a company that builds underground shelters to withstand future disasters, is repurposing the 18 square mile former military base.
It is three-quarters the size of Manhattan, New York, and access to the bunkers is through a huge heavy door.
The structures look bland from the outside - but once inside they appear to be designed like cosy front rooms.