 GEOG: The stairwell in Montmartre at the beginning of the movie lies  against a solid wall. There is no rear entrance behind that  stairwell. In addition to that, Sam is looking into the bar through  a front window. The next scene shows him coming down a flight of  stairs in a back alley but when he looks into the bar from the rear,  he is still on the same level as the bar interior though he should  be below.