Wikipedia: Natl Historic Landmarks in Maryland: Casselmans Bridge, Natl Road

Sole surviving example of the first successful all-metal bridge design to be adopted and consistently used on a railroad.

An image of the Hampton National Historic Site.

Oldest medical school building in the U.S.

An image of the Chestertown Historic District.

Built in 1930 at Charleston Drydock & Machine Co; took on the name of whatever station she was anchored at.

An image of the Antietam National Battlefield.

House where Mary Young Pickersgill sewed the large Star-Spangled Banner flag of the United States, to fly over Fort McHenry, inspiring the U.S. national anthem.

An image of the Edgar Allan Poe House and Museum.

An image of the Thomas Point Shoal Light Station.

Tollhouses built in 1835 as part of the National Road.