Cavernous docks can shelter warships, with miles of tunnels, offices, and a hospital Sweden’s navy HQ is returning to a vast underground cold war fortress designed to withstand a nuclear attack, in what has been seen as a defensive move against a resurgent Russia. After a 25-year absence, the navy will once again be commanded from beneath billions of tonnes of granite as the country strives to build up its defences in response to the perceived threat from Moscow. The top secret naval base on Muskö, about 25 miles (40km) from Stockholm, resembles a cross between Tracy Island from Thunderbirds...