Pennsylvanian mass grave and possibly mass murder.

An overlooked memorial honoring the local Washington residents who died in World War I.

Look closely and you’ll notice that the color changes a third of the way up the tower.

"Congress may voluntarily remain in session throughout the summer, in order that our Congressmen may be protected from the intolerable discomforts and dangers of the ordinary outdoor weather!”

Architecture lovers won’t stop touching the National Gallery's 19.5 degree marble prow.

This unacceptably tall building was the real reason for Washington, D.C.'s skyscraper ban.

A much-maligned monument to teetotalism.

Washington's iconic carousel has a nice piece of Civil Rights history.

Go take a picture with the inventor of the daguerreotype photographic process.

The unique traffic pattern named for an influential urban planner is also known as the Pedestrian Scramble.

The "lovely red Vega" of the legendary record-settling pilot.

Perhaps the most scandalous statue of America's first president.

Government testing at the asylum briefly explored using marijuana as a "truth serum" on Nazi prisoners of war.

A rotating cast of guys and dolls in front of a Washington, D.C. building.

People escaping slavery may have hidden inside a corpse vault.

During the Industrial Revolution this “Temple of Invention” was full of intricate miniature machines and gadgets.

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

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

This Philly cemetery is the eternal home of many famous area residents, including Rocky Balboa's wife.

The key to turning shifting dunes into the green oasis of Golden Gate Park.

Not merely a museum – but a whirring powerhouse that offers a subterranean peek into the heart and soul of cable car operations.

The last remaining relic of San Francisco's glittering 1915 Panama Pacific Exposition.

The maze-like transportation hub contains abandoned areas, derelict stores, and a resident bat colony.

This daunting 1st century fortress was purportedly the site of one of the most dramatic revolts of the Jewish-Roman wars.