Few hotels would count their blessings after unearthing a bomb shelter, but for the historic Sofitel Legend Metropole Hanoi, the discovery is turning out to be a marketing coup.

Last month, while digging the foundation for a new poolside bar, workers at the 110-year-old French-colonial hotel struck a suspiciously thick layer of concrete. According to Carl Sladen, the Metropole's sales and marketing director, there are mentions in local historic accounts of a Vietnam-era bunker designed to protect guests during air raids, but as owners and staff have changed over the years, nobody knew where it was located or if it even still existed.

'We then did some digging of a different sort,' Mr. Sladen says. 'After speaking with various contacts around Hanoi, and others who have been associated with the hotel's history, we concluded that indeed there was something down there. But we had no idea how big it was or what might be inside.'

Hotel managers instructed their engineering team to carefully excavate the site. They bored through 80 centimeters of steel-reinforced concrete, breached the bunker's ceiling and dropped in a camera.

'There wasn't much inside,' Mr. Sladen says. 'Just a few wine bottles