A gift from Scotland to the United States in memory of the 270 lives lost when Pan Am Flight 103 exploded over Lockerbie due to a terrorist bombing.

This stately mansion, built in 1787 by America's first Secretary of the Navy, is rumored to be one of the most haunted buildings in Washington, DC.

This unique historical monument features large concrete spheres designed to resemble fallen stars.

Helen Keller once broke ground on this historic center for the study of technologies to benefit the hearing impaired.

The most accurate timepiece in the world.

The site of the climactic scene from the classic horror film is now a historic landmark.

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

Parking garage where Bob Woodward met Watergate source "Deep Throat."

This historic boathouse was constructed using salvaged lumber from burned barns.

There’s a special club house at the top for the bell ringers.

The sci-fi villain is a little-known inhabitant of the U.S. capital's largest cathedral.

A tiny piece of the Moon is embedded in this stained glass masterpiece.

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

This mighty white oak in Bethesda survived both the American Revolution and the construction of Washington D.C.'s metro red line.

A derelict bit of transportation infrastructure hidden in the woods.

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

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

FDR's Art Deco hospital tower was hopelessly inefficient.

A building shaped like the Army Corps of Engineers logo, because why not?

The school tested mustard gas for the U.S. Army during World War I.

A rare example of a rural school in Washington, D.C.

The Conduit Road Schoolhouse is one of the last one-room schoolhouses remaining in Washington, D.C.

Every drop of D.C. tap water flows through this old waterworks.

A whopping 14,000 copper coins cover this miniature fighter jet.