920 N. First Ave.
If you like to push the envelope, check out this outfit that's certainly made its stamp on the Old Pueblo. This little museum houses a nationally important collection of domestic and foreign stamps, and details the history of postal deliveries from colonial days to the present. It's also a working post office (meaning it's closed on weekends); its fixtures date from late Territorial days, and the clerk sells stamps you might not easily find at your neighborhood P.O. The place also boasts a fully stocked library with info on post offices and postmasters, and if that's not enough to lick you, there's lots of civil war memorabilia and books, too.