The Steven F. Udvar-Hazy Center near Washington Dulles International Airport is the companion facility to the Museum on the National Mall.  Visitors can walk among aircraft and small artifacts in display cases located on the floor, and view aircraft hanging from the arched ceiling on elevated skywalks.  The building opened in December, 2003, and provides enough space for the Smithsonian to display the thousands of aviation and space artifacts that cannot be exhibited on the National Mall. The two sites together showcase the largest collection of aviation and space artifacts in the world.