The last holdout of a pre-Civil War rebel who took the matter of slavery into his own hands.

This advertisement for talcum powder was painted on the rock face and has since defied removal.

Built by the patriotic residents of Boonsboro in a single day.

This four-story steel sphere in Maryland was used to test biological weapons.

During World War II, blimps were a key part of the United States' defense against German U-boats—this building could house a dozen of the armed airships.

100 years later, they're still down there.

A heroic pigeon that, through a barrage of gunfire, delivered a message that saved over 100 lives in World War I.

This lovely picnic spot featuring thunderous jet landings is an aircraft spotter’s dream.

Soldiers were buried next to Lee's house in the center of Arlington Cemetery to dissuade the general from reclaiming his property after the war.

A whopping 14,000 copper coins cover this miniature fighter jet.

Ship skeletons haunt Baltimore's waterways.

Step inside Lucy, the world's largest "elephant."

This extraordinary Depression-era expenditure was modeled after a postcard of a Mediterranean hotel.

The boulder on which Alexander Hamilton laid his head after a deadly duel can still be visited on the New Jersey coast.

A tribute to the hard-working men and women of Grumman, who crafted F-14 fighter jets.

The site of a tragic massacre that spawned a multimedia franchise.

Current docking place of the SS United States, the fastest transatlantic ocean liner.

A tour de force of a fountain, memorializing a man who loved fountains more than anything else.

Tour the dark and beloved poet's former cobwebbed basement, which may have inspired "The Black Cat."

The oldest active church in Pennsylvania is also the second oldest Swedish Church in the United States.

One of Philadelphia's largest murals resides hidden under this bridge.

This 19th-century Hamptons windmill was once home to modernist painter Agnes Pelton.

A mysterious air force base built to resemble a Long Island fishing village.

This outpost of America's most popular fast-food restaurant is housed inside a palatial mansion.