The stone marker that Mason and Dixon placed at the eastern end of the famous north-south border they surveyed.

Politicians, bureaucrats, and military officers gathered in this field near the Capitol to settle their disputes with blood.

The Forest Service's surprisingly sophisticated collection of wildfire prevention art features America's most beloved bear.

A star fort along the C&O Canal in western Maryland that protected America in three wars.

This fort down the Potomac from Washington, D.C. was once the only defensive fort protecting the capital.

A Civil War Museum with some notable medical antiques.

This scenic Maryland park was the site of one of the worst prison camps of the Civil War.

Live data is transmitted from the Atlantic coast to instantly recreate the ocean waves in this fountain at the NOAA headquarters.

The longest escalator in the Western Hemisphere takes over three minutes to ride down.

Captain John Smith thought these cliffs were amazing in 1608 but sharks thought so 20 million years before him.

After hundreds of years of settlement, this once-bustling fishing village sunk into the Chesapeake Bay.

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

Bizarre Cavern.

Surrounded by industrial sprawl, a small monument marks the site of William Penn's first landing in Pennsylvania.

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

A pyramid commemorates the birthplace of James Buchanan, the 15th president of the United States

The oldest surviving presidential residence in the United States.

The home of possibly the least-loved U.S. president stands as a sort of unpopular Monticello.

The famous bell was secreted away and hidden in a church in Allentown during the British occupation of Philadelphia.

This public park was the site of the largest civilian disaster of the Civil War.

Alexander Hamilton’s creation caused quite a bit of controversy.

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

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

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