This unassuming passageway played a key role in one of the most important events in U.S. history.

This leafy estate is worth $18 million and is so grand it has two mailing addresses.

There's a crumbling old mansion inside the Smithsonian National Zoo.

There’s a hidden military meme engraved on the World War II Memorial.

A three-story tower of books about Abraham Lincoln is one of the more unusual monuments to the president.

One of the U.S. Forest Service's only mansions is outfitted with a dinner table for floating food.

The sounds of the world's largest fully functioning pipe organ dazzle shoppers at a Philadelphia Macy's.

A daily replay of the experiment that proved the rotation of the Earth.

Pennsylvanian mass grave and possibly mass murder.

This elaborate towering structure was once famed for its revolutionary height.

Its vintage camera collection gives a snapshot of the past as viewed through a photographic lens.

This park contains a number of standing stones meant to heal and inspire.

Ant sculptures march up the side of what used to be an iconic spot in punk rock lore.

A train station that was abandoned by the coal industry and was later converted into a cocktail bar.

This public space is speckled with the eerie remnants of a defunct amusement park.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.

These massive concrete balls were used to mine gold in Virginia.

One tiny triangular park commemorates the victims of a yellow fever epidemic—many of whom are buried right below the grass.

An eccentric company offers eccentric millionaires the opportunity to have spaceflight-related experiences.

This cannonball stands as a reminder of the final act of a fleeting governor amidst a revolution.

The Grand Ole Opry's big voice came from a small home in rural Virginia where she was eventually buried.