Postal History Foundation 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.