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

Largest Roman Catholic church in North America.

The beloved statue at the National Academy of Sciences is oh so inviting to sit on.

The country's oldest continually-operated mini golf course lies hidden in plain sight, eclipsed by one of D.C.'s most popular tourist attractions.

A derelict bit of transportation infrastructure hidden in the woods.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

One of the dwarven trees dates back to 1625 and survived the Hiroshima bombing.

With over 100 jam-packed rooms to explore plus elaborate tea services and events, the Mansion on O Street is a hidden treasure.

The Corinthian columns that towered over Abraham Lincoln’s inauguration stand proud.

Golden and naked, the figure that was once the highest point in New York is all that remains of the second Madison Square Garden.

The abandoned coal loading dock is a canvas for unsanctioned art.

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

An Irish Memorial commemorating those who perished due to potato blight.

One of the oldest of its kind.

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

The first American axe throwing club.

Enjoy a slice while browsing the world's largest collection of pizza memorabilia.

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

The fastest transatlantic ocean liner sat abandoned in a Philadelphia shipyard for decades.

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

Yo, Adrian!

The oldest surviving botanic garden in the United States.

The first American department store, and home to the largest operating musical instrument in the world.

A clone-tree in Washington Square Park sprung from seeds that went to the Moon and back.