Mike Chowla
Washington DC:

B&O Museum - Baltimore

Most people only know the B&O Railroad from the Monopoly board game. The B&O is short for the Baltimore and Ohio and is one of the earliest Common Carrier railroads in the United States having started in 1825. The museum chronicles the history of the B&O from the earliest days of the rail-roading to through the end of passenger era in the 1960s. If you are interested in rail, it's definitely worth a visit.