Under a glass sidewalk lie the remains of some of Manhattan's oldest buildings.

A historic cemetery with unique artwork, a Civil War fort, and also happens to be the site of the Battle of Bladensburg.

This rare triple-jurisdiction drawbridge passes through Virginia, Maryland, and Washington, D.C.

One of the only memorials dedicated to journalists who died in combat.

Remains of a historic fountain that was mysteriously lost in the demolition of a D.C. traffic circle.

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

A mammoth pair of Civil War artillery guns abandoned out in the forest.

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.

An eerie, abandoned military base engulfed by nature and graffiti is now home to a local park.

A priceless collection of the Nation's cryptologic history.

The penultimate and final resting places of British General Edward Braddock—minus a few bits and pieces.

Home of the only civilian casualty at the Battle of Gettysburg.

This monument marks the beginning journey of a wounded soldier's leg that ended up almost two states away.

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

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

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

The oldest cemetery in New Orleans, resting peacefully for over 200 years now.

The final resting place of New Orleans' most famous voodoo priestess.

Built by prisoners of war, the largest small-scale model ever built includes eight miles of tiny streams that now sit abandoned.

This iron and wood Civil War city-ship was the first vessel to be sunk by an electrically detonated torpedo.

The second-largest ceremonial mound in the United States is an artificial hill that is loosely shaped like a pentagon.

A grandiose octagonal home crowned by a large dome stands out among the antebellum mansions.

A preserved stretch of ancient fossilized trees with an impressive gem collection to boot.