An 18-mile-long tunnel for sewage waste will soon wind within the bowels of Washington, D.C.

Inside this medieval church resides a unique set of murals.

This massive sycamore tree has been labeled as one of the largest in the state.

A "house to which to flee" for settlers in colonial Pennsylvania.

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

This Art Deco service station has been providing tune-ups and turning heads for close to a century.

A museum and research center dedicated to preserving the history of Rolls-Royce and Bentley motorcars.

One of the oldest Catholic churches in the U.S., situated just east of Gettysburg.

An eccentric priest's tribute to George Washington, this chapel tells the story of the American Revolution.

The only geyser in the state of Pennsylvania is caused by pressure from an abandoned coal mine outside of the ghost town Centralia.

A pride of the state, this working museum crafts pottery mosaics in the style of Pennsylvania's earliest European settlers.

Hundreds of protractors affixed to surfaces all over the city.

A small museum along the Susquehanna River is home to a rich collection of Native American artifacts.

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

A rock maze opens up to a panoramic viewpoint at an abandoned mine full of ghost stories.

A hidden piece of Altoona's railroad history in a long-forgotten abandoned town.

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

One of the oldest of its kind.

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

North America’s largest collection of horological devices and home to a colossal clock with a dizzying array of features.

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

The last street in Pittsburgh that's paved with wood.

Pennsylvania's highest point is spotted with boulders which were pushed to the surface by nothing but cold.

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