U.S. Bureau of Engraving and Printing
Not about coins, but about paper money, but definitely worthwhile for a numismatic.
See how the buck is made! Great, informative tour for the entire family, even for those family members who do not share your hobby.
Tours start every 15 min. Beware, however, that in the peak season (from the first Monday in March until the last Friday in August) free tickets must be obtained beforehand same day: the ticket booth is located on Raoul Wallenberg Place, and opens at 8:00 a.m. and closes when all tickets have been distributed for the day.
Toll-free number: (866) 874-2330