<P> In contemporary usage, a vestibule constitutes an area surrounding the exterior door . It acts as an antechamber between the exterior and the interior structure . Often it connects the doorway to a lobby or hallway . It is the space one occupies once passing the door, but not yet in the main interior of the building </P> <P> Although vestibules are common in private residences, as a modified mud room, they are especially prevalent in more opulent buildings, such as government ones, designed to elicit a sense of grandeur by contrasting the vestibule's small space with the following greater one, and by adding the aspect of anticipation . The residence of the White House in the United States is such an example, but somewhat confusing . At the north portico, it contains a tiny vestibule now between the doors flushed with the outer and inner faces of the exterior wall of, and in the past inside, the Entrance Hall (called incorrectly Vestibule) separated from the not much bigger Cross Hall by just 2 double columns . The difference in sizes between a vestibule and the following space is better illustrated by the--so called--entrance (15) to the main gallery in the Solomon R. Guggenheim Museum by Frank Lloyd Wright . Many government buildings mimic the classical architecture from which the vestibule originates . </P> <P> A purely utilitarian use of vestibules in modern buildings is to create an "air lock" entry . Such vestibules consist of merely a set of inner doors and a set of outer doors, the intent being to reduce air infiltration to the building by having only one set of doors open at any given time . </P> <P> An ATM vestibule is an enclosed area with automated teller machines that is accessible from the outside of a building, but typically features no further entrance beyond the vestibule . There may be a secure entrance to the vestibule which requires a card to open . </P>

What is the space between two sets of doors called