An American flag was erected for every day that passed during the Iranian Hostage Crisis.

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

The slate extracted from these Pennsylvania quarries was once hailed as the finest in the world.

This strange, big-tailed beast became a Pennsylvania town's unofficial mascot.

This 19th century machine put animals (including humans) in boxes to study how they metabolized calories.

The site of America's first commercial oil well essentially disappeared after the town went bust.

Each step is a mere four inches tall, said to be measured by the stride of a woman wearing a hobble skirt.

The aggressively banal name of this underground fortress of bureaucracy does little to evoke its truly surreal existence.

Sections of the iconic limestone columns have been left uncleaned as a reminder of the city's polluted past.

The site of the little-known Pennsylvania battle that sparked the Seven Years' War.

The only statue of its kind to commemorate Washington's beginnings as an officer of the British Colonial Militia.

No one knows who painted this mysterious mural in a Penn State basement.

This stately 19th century library pushed architectural boundaries at a time when the public library movement was just taking off.

The largest clock face in the United States is twice the size of Big Ben and infinitely more ad-sponsored.

This forgotten building was one of the few Philadelphia-area breweries to survive Prohibition.

The Cold War-era "underground Pentagon" is a sprawling subterranean hideaway for the Defense Department.

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

This giant disembodied horse head seems to balance impossibly on its nose.

A museum commemorating the Donora Smog, which killed 20 people in October 1948 and sparked national outrage over air pollution.

A preserved 18th century homestead in Western Pennsylvania marks the spot where the Whiskey Rebellion began.

Contrary to popular belief, this secluded statue doesn't represent Pennsylvania's founder.

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.

According to local myth this cemetery is half evil spirits, half good—split down the middle.

A diorama of the Civil War, fought by cats.