The highway's southernmost spot is a beloved local attraction.

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

An eerie, decaying ghost town destined to fade into the forest.

The highest point in Delaware is located under a trailer so this marker across the street will have to do.

Berthed at the Charlestown Navy Yard in Boston, "Old Ironsides" is the oldest commissioned warship still afloat.

Three and a half miles of cliffs, rocky beaches, Gilded Age mansions and 40 Steps to nowhere in particular.

This extraordinary Depression-era expenditure was modeled after a postcard of a Mediterranean hotel.

The tombstone of the founder of the lost town of Ogletown is now stuck inside a traffic median.

The man who first patented the Ouija board rests in peace beneath a headstone that playfully reflects that achievement.

A blank headstone topped with a pile of pennies marks the final resting place of the infamous assassin.

What began as an art installation is now the private drinkhaüs for a brewery's employees.

This taxidermy horse was a Civil War hero.

There’s a hidden military meme engraved on the World War II Memorial.

The most decorated dog of World War I is preserved in the Smithsonian.

This bleach-white graveyard overlooking the ocean is accessed through a tunnel.

Once America's tallest structure, now a Baltimore landmark.

From this desk Al Hirschfeld drew his influential caricatures of the 20th century's Broadway stars.

Two large-scale sculptures of Adam and Eve greet visitors in the nude at the Time Warner Center in NYC.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

Washington's iconic carousel has a nice piece of Civil Rights history.

The tunnel under the Capitol Building where Congress takes out its trash.

The 5.5-mile ring of steel posts around the Capitol Building is one of the largest (and most uniform) of its kind in the world.

A hidden gem on the lawn of the U.S. Capitol Building designed by landscape architect Frederick Law Olmsted.

Built by the patriotic residents of Boonsboro in a single day.