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

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.

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

The first of Lancaster's "rural cemeteries."

This colonial mansion has been home to a staggering number of American historic figures.

Where the oil industry began.

Memorializing an American tragedy of massive proportions.

Pittsburgh's literal underground railroad.

Meet your friends, marry your true love, or tell your enemies to kiss your butt under this historic Pittsburgh timepiece.

This picturesque stream was up until recently the site of a ten story mountain of slag and sewage.

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

What looks like a simple quaint estate in rural Pennsylvania was in the 18th century home to a small monastic community.

Erected in 1697 this Philadelphia bridge is the oldest surviving roadway bridge and perhaps the oldest stone bridge in the United States.

One of the oldest of its kind.

An 18th-century Catholic church converted into an eccentric temple of music and bacchanalia.

A living maritime paradox still floats in the same lake where it was built and resurrected... or was it?

An ideal wedding spot that is almost too ideal.

This huge, disused viaduct is now a crumbling concrete underworld of covered in years of graffiti.

A planned settlement in Pennsylvania once housed the aristocratic refugees of the French Revolution.

A museum dedicated to the history & joys of the trail & your best chance to see hikers throwing up ice cream.

This collection honors the iconic, and proudly American lighter that just won't quit.

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

This jail which was in service for over a century is now open for curious visitors.