Color-coded signs direct drivers on a network of routes designed to avoid Pittsburgh traffic.

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

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

One of the oldest of its kind.

This meticulously extracted nervous system allegedly came from a 19th-century custodian who donated her body to science.

A dramatic, 360-degree recreation of Pickett's Charge in the Civil War.

Gnarled canopies of pink and purple wildflowers arch over the trail to the summit.

One of the most influential presidents in U.S. history wanted only this plain, elegant monument as his lasting memorial.

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

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

Edison's cast-in-place concrete houses were a failure, but way ahead of their time.

The lecture hall where Alexander Graham Bell first demonstrated the long-distance phone call.

This palatial botanical garden is home to one of the largest pipe organs ever installed in a private residence, and a piece of Wood's cycad.

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

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.

During the summer, surfers in Alaska take advantage of this inlet’s unusual water patterns.

Four-story concrete hotel never opened to customers.

A railroad magnate's replica village has become home to a genetic seed bank for rare breeds of livestock.

Mysterious stone tower featured in many alternative histories of the New World.

An organ located deep within a cave, whose "pipes" are the geological features of the cave itself.

Public outcry led to this bridge's unique character which celebrates a giant frog battle and also sewing.

One of the now-less-hidden floral gems of the "Emerald Necklace."

This headstone marks the grave of an 11-year-old boy killed during clashes in the streets over the boycotting of British goods.

The oldest working bell set in North America, the bells at Old North Church sat silent for their first four years in Massachusetts.