I have sung the National Anthem at a large variety of events, and have often heard the flag-folding story about how Francis Scott Key, watching the British bombardment of Fort McHenry during the War of 1812 was inspired to pen the poem that later became the U.S. National Anthem. The opportunity to visit was a treat.
The property is rather small and mostly obscured by surrounding neighborhoods and the shipyards, but it's not difficult to get to from the interstate. Once on the grounds, it opens up with a large, beautiful lawn and trees with one historical building near the entrance, the main museum and the fort at the far end near the river. After parking, I went inside and toured the small museum and watched a short historical video re-enactment of fort bombardment.
Short but thorough, the building exhibit is a concise tale of the war, the state of U.S. culture and the germination of the anthem from the shelling, penning and distributing the poem and its finalization through various wars and other events.
The fort, itself, is a traditional historical star fort with multiple layers of defenses surrounding an interior yard with buildings hosting a variety of historical lifestyle and military exhibits. Everything is very well preserved and rather beautiful.
Despite all the modern shipyards up and down the coasts, it's almost easy to see the 30 British warships sailing up the inlet, turning broadside and opening fire on the fort, and the U.S. soldiers and sailors scrambling to return fire and keep the British from the mouth of the harbor leading into Baltimore, and how after the shelling they hoisted the massive flag that now sits at the National Museum of American History in DC.
This is definitely a place worth visiting if you love American history. There's not a lot to it, but you'll get a lot out of it.