America's History is in The Mail

The National Postal Museum, a Smithsonian Institution museum, is located in the old Post Office building next to Union Station in Washington, D.C. The Museum was created by an agreement between the Smithsonian Institution and the United States Postal Service in 1990 and opened to the public in 1993.
The Museum is open seven days a week from 10 a.m. to 5:30 p.m., except December 25. Admission is free.