An airlock entryway (vestibule) has two airtight doors that reduce the amount of air infiltration and heat loss when the exterior door is opened. They create a buffer area to block the wind and improve energy efficiency. Double door airlock entries are common features in energy-efficient homes in cold climates, but they also reduce air conditioning costs in hot climates. The airlock entryway shown above includes two insulated doors, coat closet, washer and dryer with shelves, window for daylighting, and a bench for changing shoes. The Popular Science article linked below shows four ways to build airlock entries.