Shangri-la was a place of mystery; a utopia.
The place was fictional, some mysterious region in Tibet conceived by the late English-born novelist, James Hilton, in Lost Horizon (1933), where people lived for hundreds of years and attempted to preserve the best achievements in art and ideals of the outside world despite its tensions.
The concept gained widespread appeal.
Thus when, in World War II, President F. D. Roosevelt smilingly told reporters that the flyers under General James Doolittle in the bombing of Tokyo had taken off from Shangri-la, it was immediately understood that the point of departure was not to be made public, was to remain as undisclosed as Hilton’s place of mystery.