If you're interested in mail or in direct marketing, you'll find the Smithsonian's National Postal Museum fascinating.
This weekend I was up visiting DC with my family. The big Smithsonian museums were mobbed -- school break week -- so we headed off the mall to the smaller museums.
The National Postal Museum is a real gem. The museum is located about a mile from the mall, right across from the Union Station stop on the Metro's red line. It is very kid friendly, with historic exhibits on the Pony Express, modern adventures of gun-toting postal inspectors, demos of modern lettershop equipment, interactive games on the list industry, etc. The architecture is airy and beautiful. (For mailers bracing for the postal rate tsunami hitting May 14th: this museum is part of the Smithsonian, so the lavish space and exhibits didn't drain USPS coffers.)
I enjoyed the museum as much as my kids, maybe even more so. I knew little about postal history going in. I hadn't known that in the revolutionary era a robust postal system was considered as essential to the colonies as freedom of the press. Hadn't known the colorful history of the pony express, or of the postal inspectors. Hadn't known much about the origins of rural free delivery (RFD) in 1896, where farm families demanded that Congress fund delivery beyond rural post offices all the way to the farm houses, and how RFD's rollout in 1902 drove the development of much of the rural road network. Hadn't known all that much about the birth of the catalog industry and the importance of mail order to American farm families. (Neat to see catalogs from two RKG clients from 130 years ago!)
Next time you have a spare hour in DC, consider visiting the National Postal Museum across from Union Station. Though small, it is a true Smithsonian gem.