The former home of Thomson Francis Mason, the mayor of Alexandria from 1827-1830.

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

America's first federal monument.

This cannon dating to 1755 has stood guard at this suburban intersection since 1915.

The only labyrinth within the city of Alexandria.

A small and somewhat hidden memorial to 68 local veterans of the Vietnam War.

This site is believed to be connected to the oldest house in Arlington County.

When it comes to handsignals (and colonialism) rock always beats scissors.

The most accurate timepiece in the world.

A hoard of sky catalogs, astrophysical journals, even the works of Galileo and Copernicus.

A painfully obvious spy house sits right across the street from the Russian Embassy.

The only Civil War battle in Washington D.C. took place near this highest natural point in the city.

Washington's top-secret Cold War-era doomsday communications tower is located in a small neighborhood park.

Surrounded by traditional homes, this Tolkien-esque dwelling stands out on a quiet street in suburban Maryland.

This forgotten boat elevator was an engineering marvel in its heyday.

One of the few surviving examples of the first lock and dam system built on the Ohio River.

This campus chapel is Robert E. Lee's final resting place and a topic of debate about the legacy of the Civil War.

One of the few places where you can explore a 1918 paddlewheel steamboat from stem to stern.

What started as a display of antique hearses has grown into a museum exploring the history of the funeral industry.

This university transit system is a 1970's vision of the future.

The brainchild of Eleanor Roosevelt, her "Little Village" was a collectivist dream.

Spectacular mineral formations fill these caves, which have been used for everything from smoking meat to stashing illicit liquor.

A memorial honoring those who perished in one of the worst construction disasters in U.S. history.

A historic coal mine that doubles as a museum and tourist attraction.