Fort Whetstone, the original fort defended Baltimore between 1776 and 1797. It was replaced with Fort McHenry. Fort McHenry was named after James McHenry (1753–1816), a delegate to the Continental Convention.

The Fort successfully defended Baltimore against the British during the War of 1812 and during that battle is when Frances Scott Key wrote the Star-Spangled Banner. It was later used during the Civil War as a prison for Confederate Soldiers. 

Definitely a must see when visiting Baltimore. Your tour begins in the Welcome Center with a nicely done movie about the history of the Fort. After that the tour is self-guided and leads you through out the Fort. Many rooms have been set up as examples of how they were used during the 1812 War.

2400 East Fort Avenue, Baltimore, MD 21230

Check their web site for hours and closures during holidays. 

https://www.nps.gov/fomc/planyourvisit/basicinfo.htm
https://www.nps.gov/fomc/index.htm

Admission is $15 and children under 15 are free.