KOSTYANTYNIVKA, Ukraine—On the sun-drenched eastern front of this grueling war, Ukrainian drones are doing more and more jobs ...

In the 1960s, a private courtyard in central London had a water fountain that could slide sideways to reveal the entrance to a vast complex of secret tunnels.

Switzerland, which has a population of 8.8 million, has over 370,000 nuclear shelters, more per capita than anywhere else on ...