A historic ruin just 20 feet away from a busy highway onramp.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

This imposing Masonic temple a mile from the White House was the first public library in Washington, D.C.

The quarry was abandoned over 100 years ago, after a massive ammunition explosion ended in tragedy.

Abandoned rock quarry now a haven for mountain bikers and hikers.

A derelict bit of transportation infrastructure hidden in the woods.

The United States Capitol's former columns still stand.

The site of the climactic scene from the classic horror film is now a historic landmark.

This historic Pittsburgh tennis complex is a rare example of natural red clay courts.

A portion of the old Pirates stadium over which a defining home run once flew still stands even after the rest of the stadium was torn down.

A model of a dinosaur that was named for Andrew Carnegie stands outside the museum that also bears his name.

There aren't too many operational funiculars around, but Pittsburgh has two!

One of the steepest streets in the United States makes an intriguing challenge for cyclists.

A cave on the Maryland border where civilians took refuge during the bloodiest battle of the Civil War.

A monument marks the location of the first successful steamboat demonstration.

America's smallest national park site is the former residence of exiled Polish national hero Thaddeus Kosciuszko.

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

Yo, Adrian!

A secret greenspace hides atop a Capitol parking garage.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

This statue of the "father of television" stands prominently in the United States Capitol.

One critic described it as "middle Mussolini, early Ramses, and late Neiman-Marcus." Another called it an architectural "natural disaster."

The little-known, 300-year history of the area includes former lives as a bustling tobacco port, parking lot, and industrial dump.

A tiny monument to the unsuccessful attempt by Thomas Jefferson to place the prime meridian in Washington.