HANOI (AP).- The siren’s wail at the historic Metropole Hotel sent American folk singer Joan Baez and other guests scampering across a garden and into an underground bunker. Even through five feet of concrete, they could still hear the roar of American bombs raining on parts of Hanoi. Nearly four decades have passed since the so-called Christmas Bombings rocked parts of Vietnam’s capital in December 1972. After the war ended three years later, the bunker was sealed and all but forgotten. Its exact location remained a mystery until this summer, when a worker’s drill pierced its thick concrete roof during renovations of a poolside bar. Since then, workers have been excavating the flooded and low-ceilinged space. Not much has been found in the seven rooms: a wine bottle, a rusty paint can and a light bulb still in a socket. But a few tales remain, some involving famous guests. “If these walls could talk, they would tell a lot of stories,” says hotel general manager Kai Speth, while